Galectin-3 binds Neisseria meningitidis and increases interaction with phagocytic cells

Genome-wide characterization, phylogenetic and expression analysis of Galectin gene family in Golden pompano Trachinotus ovatus

Galectins (Gals) are a type of S-type lectin that are widespread and evolutionarily conserved among metazoans, and can act as pattern recognition receptors (PRRs) to recognize pathogen-associated molecular patterns (PAMPs). In this study, 10 Gals (ToGals) were identified in the Golden pompano (Trachinotus ovatus), and their conserved domains, motifs, and collinearity relationships were analyzed. The expression of ToGals was regulated following infection to Cryptocaryon irritans and Streptococcus agalactiae, indicating that ToGals participate in immune responses against microbial pathogens. Further analysis was conducted on one important member, Galectin-3, subcellular localization showing that ToGal-3like protein is expressed both in the nucleus and cytoplasm. Recombinant protein obtained through prokaryotic expression showed that rToGal-3like can agglutinate red blood cells of rabbit, carp and golden pompano and also agglutinate and kill Staphylococcus aureus, Bacillus subtilis, Vibrio vulnificus, S. agalactiae, Pseudomonas aeruginosa, and Aeromonas hydrophila. This study lays the foundation for further research on the immune roles of Gals in teleosts.

Serum galectin-3 levels predict poor prognosis in sepsis and septic shock patients

OBJECTIVE

Sepsis and septic shock are clinical conditions with high mortality and an ever-increasing prevalence, and early diagnosis is of great importance in treating these diseases. Increase in serum Galectin-3 protein in septic patients is associated with increased inflammation, which in turn is associated with mortality. This study aimed to investigate the diagnostic importance of serum Galectin-3 levels and its relationship with in-hospital mortality in sepsis and septic shock patients.

METHODS

This prospective cohort study included 44 sepsis and 44 septic shock patients. Sequential Organ Failure Assessment score and Acute Physiology and Chronic Health Evaluation 2 score were calculated. In addition, routine clinical and laboratory parameters along with serum Galectin-3 were evaluated.

RESULTS

Serum Galectin-3 levels were significantly higher in the septic shock group [4.1 (0.1-10.2) vs. 6.0 (0.1-11.3) ng/mL, respectively; p=0.01]. Moreover, patients with a Galectin-3 level <6.94 ng/mL were associated with longer survival [31.4 vs. 23.1 days; hazards ratio, 1.85; 1.03-3.34, p=0.03]. More importantly, the need for mechanical ventilation, the duration of mechanical ventilation, and serum Galectin-3 levels were independent prognostic factors and predicted poor in-hospital survival in both sepsis and septic shock patients.

CONCLUSION

These findings suggest that Galectin-3 levels are higher in septic shock patients and predict mortality. In addition, high serum Galectin-3 levels, together with mechanical ventilation requirement and mechanical ventilation duration, are closely associated with poor in-hospital survival. Therefore, Galectin-3 may be a valuable diagnostic and prognostic biomarker in these patients.

Deficiency in Galectin-3, -8, and -9 impairs immunity to chronic Mycobacterium tuberculosis infection but not acute infection with multiple intracellular pathogens

Macrophages employ an array of pattern recognition receptors to detect and eliminate intracellular pathogens that access the cytosol. The cytosolic carbohydrate sensors Galectin-3, -8, and -9 (Gal-3, Gal-8, and Gal-9) recognize damaged pathogen-containing phagosomes, and Gal-3 and Gal-8 are reported to restrict bacterial growth via autophagy in cultured cells. However, the contribution of these galectins to host resistance during bacterial infection in vivo remains unclear. We found that Gal-9 binds directly to Mycobacterium tuberculosis (Mtb) and Salmonella enterica serovar Typhimurium (Stm) and localizes to Mtb in macrophages. To determine the combined contribution of membrane damage-sensing galectins to immunity, we generated Gal-3, -8, and -9 triple knockout (TKO) mice. Mtb infection of primary macrophages from TKO mice resulted in defective autophagic flux but normal bacterial replication. Surprisingly, these mice had no discernable defect in resistance to acute infection with Mtb, Stm or Listeria monocytogenes, and had only modest impairments in bacterial growth restriction and CD4 T cell activation during chronic Mtb infection. Collectively, these findings indicate that while Gal-3, -8, and -9 respond to an array of intracellular pathogens, together these membrane damage-sensing galectins play a limited role in host resistance to bacterial infection.

Vertebrate and Invertebrate Animal and New In Vitro Models for Studying Neisseria Biology

The history of Neisseria research has involved the use of a wide variety of vertebrate and invertebrate animal models, from insects to humans. In this review, we itemise these models and describe how they have made significant contributions to understanding the pathophysiology of Neisseria infections and to the development and testing of vaccines and antimicrobials. We also look ahead, briefly, to their potential replacement by complex in vitro cellular models.

Respiratory Viruses and Cystic Fibrosis

The threat of respiratory virus infection to human health and well-being has been clearly highlighted by the coronavirus disease 2019 (COVID-19) pandemic. For people with cystic fibrosis (CF), the clinical significance of viral infections long predated the emergence of severe acute respiratory syndrome coronavirus 2. This article reviews the epidemiology, diagnosis, and treatment of respiratory virus infection in the context of CF as well as the current understanding of interactions between viruses and other microorganisms in the CF lung. The incidence of respiratory virus infection in CF varies by age with young children typically experiencing more frequent episodes than adolescents and adults. At all ages, respiratory viruses are very common in CF and are associated with pulmonary exacerbations. Respiratory viruses are identified at up to 69% of exacerbations, while viruses are also frequently detected during clinical stability. The full impact of COVID-19 in CF is yet to be established. Early studies found that rates of COVID-19 were lower in CF cohorts than in the general population. The reasons for this are unclear but may be related to the effects of shielding, infection control practices, maintenance CF therapies, or the inflammatory milieu in the CF lung. Observational studies have consistently identified that prior solid organ transplantation is a key risk factor for poor outcomes from COVID-19 in CF. Several key priorities for future research are highlighted. First, the impact of highly effective CFTR modulator therapy on the epidemiology and pathophysiology of viral infections in CF requires investigation. Second, the impact of respiratory viruses on the development and dynamics of the CF lung microbiota is poorly understood and viral infection may have important interactions with bacteria and fungi in the airway. Finally, bacteriophages represent a key focus of future investigation both for their role in transmission of antimicrobial resistance and as a promising treatment modality for multiresistant pathogens.

G1 Cell Cycle Arrest Is Induced by the Fourth Extracellular Loop of Meningococcal PorA in Epithelial and Endothelial Cells

Neisseria meningitidis is the most frequent cause of bacterial meningitis and is one of the few bacterial pathogens that can breach the blood-brain barrier (BBB). The 37/67 kDa laminin receptor (LamR) was previously identified as a receptor mediating meningococcal binding to rodent and human brain microvascular endothelial cells, which form part of the BBB. The meningococcal surface proteins PorA and PilQ were identified as ligands for this receptor. Subsequently, the fourth extracellular loop of PorA (PorA-Loop4) was identified as the LamR-binding moiety. Here, we show that PorA-Loop4 targets the 37 kDa laminin receptor precursor (37LRP) on the cell surface by demonstrating that deletion of this loop abrogates the recruitment of 37LRP under meningococcal colonies. Using a circularized peptide corresponding to PorA-Loop4, as well as defined meningococcal mutants, we demonstrate that host cell interaction with PorA-Loop4 results in perturbation of p-CDK4 and Cyclin D1. These changes in cell cycle control proteins are coincident with cellular responses including inhibition of cell migration and a G1 cell cycle arrest. Modulation of the cell cycle of host cells is likely to contribute to the pathogenesis of meningococcal disease.

Molecular characterization, immune responses, and functional aspects of atypical prototype galectin from redlip mullet (Liza haematocheila) as a pattern recognition receptor in host immune defense system

Galectins are a family of lectins that are widely distributed β-galactoside-binding proteins identified in diverse organisms. Galectin family have appeared as pattern recognition receptors (PRRs) responsible for initiating and controlling the innate immunity. The present study aimed to study the binding ability and potential role in PRRs of galectin-related protein B-like (LhGal B-like) from redlip mullet (Liza haematocheila) involved in the host immune responses. We constructed a cDNA library of redlip mullet and identified the LhGal B-like sequence. By sequence analysis and multiple sequence alignment, we revealed that LhGal B-like contains a conserved carbohydrate recognition domain (CRD) and consists of 135 amino acids with a predicted molecular weight of 16.07 kDa. In addition, pairwise comparison results showed that LhGal B-like shares higher sequence identity (82.2-95.2%) and similarity (89-95.9%) with fish species than those (34.1-37.8% and 57.2-58.1%, respectively) with other species. The phylogenetic tree showed that LhGal B-like clustered into the fish group and was evolutionally related to Mastacembelus armatus. The tissue distribution results revealed that LhGal B-like was expressed ubiquitously in all the tested tissues, where it was highly expressed in the brain, followed by gills and muscle. The immune modulated expression of LhGal B-like was observed by injecting lipopolysaccharide (LPS), polyinosinic:polycytidylic acid (poly I:C) and Lactococcus garvieae (L. garvieae). According to the results, in the gills, the mRNA expression of LhGal B-like was significantly upregulated upon LPS treatment after 48 h and upon poly I:C treatment after 48 and 72 h. In addition, the result showed significant upregulations upon LPS and poly I:C treatment after 24 h. However, significant downregulation was also shown in the earlier phase after injection of poly I:C and L. garvieae in gills. Further, the binding affinity of recombinant LhGal B-like (rLhGal B-like) was evaluated using carbohydrate, pathogen-associated molecular patterns (PAMP) and bacterial binding assays. The rLhGal B-like could bind all the examined carbohydrates but had a higher affinity to α-lactose. PAMPs and bacterial binding experiments verified a wide range of PAMP molecules and bacterial strains that rLhGal B-like could bind to. Moreover, we examined the agglutination activity of rLhGal B-like, and the result showed that it could aggregate all the gram-positive and gram-negative bacteria. Taken together, our findings reveal the functional aspects of LhGal B-like as a PRR and the potential involvement of LhGal B-like in the innate immunity of redlip mullet.

The role of galectins in immunity and infection

The galectin family consists of carbohydrate (glycan) binding proteins that are expressed by a wide variety of cells and bind to galactose-containing glycans. Galectins can be located in the nucleus or the cytoplasm, or can be secreted into the extracellular space. They can modulate innate and adaptive immune cells by binding to glycans on the surface of immune cells or intracellularly via carbohydrate-dependent or carbohydrate-independent interactions. Galectins expressed by immune cells can also participate in host responses to infection by directly binding to microorganisms or by modulating antimicrobial functions such as autophagy. Here we explore the diverse ways in which galectins have been shown to impact immunity and discuss the opportunities and challenges in the field.

Galectins: An Ancient Family of Carbohydrate Binding Proteins with Modern Functions

Galectins are a large family of carbohydrate binding proteins with members in nearly every lineage of multicellular life. Through tandem and en-mass genome duplications, over 15 known vertebrate galectins likely evolved from a single common ancestor extant in pre-chordate lineages. While galectins have divergently evolved numerous functions, some of which do not involve carbohydrate recognition, the vast majority of the galectins have retained the conserved ability to bind variably modified polylactosamine (polyLacNAc) residues on glycans that modify proteins and lipids on the surface of host cells and pathogens. In addition to their direct role in microbial killing, many proposed galectin functions in the immune system and cancer involve crosslinking glycosylated receptors and modifying signaling pathways or sensitivity to antigen from the outside in. However, a large body of work has uncovered intracellular galectin functions mediated by carbohydrate- and non-carbohydrate-dependent interactions. In the cytoplasm, galectins can tune intracellular kinase and G-protein-coupled signaling cascades important for nutrient sensing, cell cycle progression, and transformation. Particularly, but interconnected pathways, cytoplasmic galectins serve the innate immune system as sensors of endolysosomal damage, recruiting and assembling the components of autophagosomes during intracellular infection through carbohydrate-dependent and -independent activities. In the nucleus, galectins participate in pre-mRNA splicing perhaps through interactions with non-coding RNAs required for assembly of spliceosomes. Together, studies of galectin function paint a picture of a functionally dynamic protein family recruited during eons of evolution to regulate numerous essential cellular processes in the context of multicellular life.

Full-Length Galectin-3 Is Required for High Affinity Microbial Interactions and Antimicrobial Activity

While adaptive immunity enables the recognition of a wide range of microbial antigens, immunological tolerance limits reactively toward self to reduce autoimmunity. Some bacteria decorate themselves with self-like antigens as a form of molecular mimicry to limit recognition by adaptive immunity. Recent studies suggest that galectin-4 (Gal-4) and galectin-8 (Gal-8) may provide a unique form of innate immunity against molecular mimicry by specifically targeting microbes that decorate themselves in self-like antigens. However, the binding specificity and antimicrobial activity of many human galectins remain incompletely explored. In this study, we defined the binding specificity of galectin-3 (Gal-3), the first galectin shown to engage microbial glycans. Gal-3 exhibited high binding toward mammalian blood group A, B, and αGal antigens in a glycan microarray format. In the absence of the N-terminal domain, the C-terminal domain of Gal-3 (Gal-3C) alone exhibited a similar overall binding pattern, but failed to display the same level of binding for glycans over a range of concentrations. Similar to the recognition of mammalian glycans, Gal-3 and Gal-3C also specifically engaged distinct microbial glycans isolated and printed in a microarray format, with Gal-3 exhibiting higher binding at lower concentrations toward microbial glycans than Gal-3C. Importantly, Gal-3 and Gal-3C interactions on the microbial microarray accurately predicted actual interactions toward intact microbes, with Gal-3 and Gal-3C displaying carbohydrate-dependent binding toward distinct strains of Providentia alcalifaciens and Klebsiella pneumoniae that express mammalian-like antigens, while failing to recognize similar strains that express unrelated antigens. While both Gal-3 and Gal-3C recognized specific strains of P. alcalifaciens and K. pneumoniae, only Gal-3 was able to exhibit antimicrobial activity even when evaluated at higher concentrations. These results demonstrate that while Gal-3 and Gal-3C specifically engage distinct mammalian and microbial glycans, Gal-3C alone does not possess antimicrobial activity.

Galectin-3 as a modifier of anti-microbial immunity: Unraveling the unknowns

Galectins play diverse roles in pathophysiology of infectious diseases and cancers. Galectin-3 is one of the most studied family member and the only chimeric type lectin. Many aspects of its biogenesis, range of activities, and the disease-modifying potential particularly during microbial infections are yet to be known. We review our current understanding of these issues and also highlight gaps in better defining the immune modulatory potential of galectin-3 during different stages of host responsiveness when an infection sets in. Additionally, we discuss commonly used strategies to disrupt galectin-3 functions both extracellulalry and intracellularly. Existing and improved novel strategies could help fine-tune immune responses to achieve better prognosis of infectious diseases.

Galectin-3 plays a protective role in Leishmania (Leishmania) amazonensis infection

Leishmania (L.) amazonensis is one of the species responsible for the development of cutaneous leishmaniasis in South America. After entering the vertebrate host, L. (L.) amazonensis invades mainly neutrophils, macrophages, and dendritic cells. Studies have shown that gal-3 acts as a pattern recognition receptor. However, the role of this protein in the context of L. (L.) amazonensis infection remains unclear. Here, we investigated the impact of gal-3 expression on experimental infection by L. (L.) amazonensis. Our data showed that gal-3 plays a role in controlling parasite invasion, replication and the formation of endocytic vesicles. Moreover, mice with gal-3 deficiency showed an exacerbated inflammatory response. Taken together, our data shed light to a critical role of gal-3 in the host response to infection by L. (L.) amazonensis.

Galectin-3 regulates proinflammatory cytokine function and favours Brucella abortus chronic replication in macrophages and mice

In this study, we provide evidence that galectin-3 (Gal-3) plays an important role in Brucella abortus infection. Our results showed increased Gal-3 expression and secretion in B. abortus infected macrophages and mice. Additionally, our findings indicate that Gal-3 is dispensable for Brucella-containing vacuoles disruption, inflammasome activation and pyroptosis. On the other hand, we observed that Brucella-induced Gal-3 expression is crucial for induction of molecules associated to type I IFN signalling pathway, such as IFN-β: Interferon beta (IFN-β), C-X-C motif chemokine ligand 10 (CXCL10) and guanylate-binding proteins. Gal-3 KO macrophages showed reduced bacterial numbers compared to wild-type cells, suggesting that Gal-3 facilitates bacterial replication in vitro. Moreover, priming Gal-3 KO cells with IFN-β favoured B. abortus survival in macrophages. Additionally, we also observed that Gal-3 KO mice are more resistant to B. abortus infection and these animals showed elevated production of proinflammatory cytokines when compared to control mice. Finally, we observed an increased recruitment of macrophages, dendritic cells and neutrophils in spleens of Gal-3 KO mice compared to wild-type animals. In conclusion, this study demonstrated that Brucella-induced Gal-3 is detrimental to host and this molecule is implicated in inhibition of recruitment and activation of immune cells, which promotes B. abortus spread and aggravates the infection. TAKE AWAYS: Brucella abortus infection upregulates galectin-3 expression Galectin-3 regulates guanylate-binding proteins expression but is not required for Brucella-containing vacuole disruption Galectin-3 modulates proinflammatory cytokine production during bacterial infection Galectin-3 favours Brucella replication.

Galectin-3 in Critically Ill Patients with Sepsis and/or Trauma: A Good Predictor of Outcome or Not?

Severe sepsis and/or trauma complicated with multiple organ dysfunction syndrome are leading causes of death in critically ill patients. The aim of this prospective, observational, single centre study was to assess the prognostic value of galectin-3 regarding outcome in critically ill patients with severe trauma and/or severe sepsis. The outcome measure was hospital mortality.

In total, 75 critically ill patients who were admitted to the intensive care unit of the tertiary university hospital were enrolled in a prospective observational study. Blood samples were collected upon fulfilling Sepsis-3 criteria and for a traumatized Injury Severity Score > 25 points.

Levels of galectin-3 were significantly higher in nonsurvivors on the day of enrolment – Day 1 (p<0.05). On Day 1, the area under the curve (AUC) for the galectin-3 for lethal outcome was 0.602. At a cut-off level of 262.82 ng/mL, the sensitivity was 53%, and the specificity was 69.7%, which was objectively determined by a Youden index of 0.20.

The discriminative power of galectin-3 in predicting outcome was statistically significant. Galectin-3 on Day 1 is a fairly good predictor of lethal outcome.

Galectin-3, Possible Role in Pathogenesis of Periodontal Diseases and Potential Therapeutic Target

Periodontal diseases are chronic inflammatory diseases that occur due to the imbalance between microbial communities in the oral cavity and the immune response of the host that lead to destruction of tooth supporting structures and finally to alveolar bone loss. Galectin-3 is a β-galactoside-binding lectin with important roles in numerous biological processes. By direct binding to microbes and modulation of their clearence, Galectin-3 can affect the composition of microbial community in the oral cavity. Galectin-3 also modulates the function of many immune cells in the gingiva and gingival sulcus and thus can affect immune homeostasis. Few clinical studies demonstrated increased expression of Galectin-3 in different forms of periodontal diseases. Therefore, the objective of this mini review is to discuss the possible effects of Galectin-3 on the process of immune homeostasis and the balance between oral microbial community and host response and to provide insights into the potential therapeutic targeting of Gal-3 in periodontal disease.

Galectins in turbot (Scophthalmus maximus L.): Characterization and expression profiling in mucosal tissues

Galectins, a family of evolutionary conserved β-galactoside-binding proteins, have been characterized in a wide range of species. Many reports have indicated vital roles of galectins in innate immunity, especially in the mucosal tissues against infection. However, the systematic identification of galectin gene family is still lacking in teleost. Here, we characterized the galectin gene family and investigated their expression profiles post bacterial challenge in turbot (Scophthalmus maximus L.). In this study, a total of 13 galectin genes were characterized in turbot, phylogenetic analyses revealed their strong relationships to half smooth tongue sole and puffer fish, and syntenic analyses confirmed the orthology suggested by the phylogenetic analysis. In addition, the copy number of galectin genes is similar across a broad spectrum of species from fish to amphibians, birds, and mammals, ranging from 8 to 16 genes. Furthermore, the galectin genes were widely expressed in all the examined turbot tissues, and most of the galectin genes were strongly expressed in mucosal tissues (skin, gill and intestine). Moreover, majority of the galectin genes were significantly regulated after Vibrio anguillarum infection in the intestine, gill and skin, suggesting that galectins were involved in the mucosal immune response to V. anguillarum infection in turbot. In addition, subcellular localization analysis showed lgals3a was distributed in the cytoplasm and nucleus. However, the knowledge of galectins are still limited in teleost species, further studies should be carried out to better characterize its detailed roles in teleost mucosal immunity.

Long-term skin-resident memory T cells proliferate in situ and are involved in human graft-versus-host disease

The skin contains a population of tissue-resident memory T cells (Trm) that is thought to contribute to local tissue homeostasis and protection against environmental injuries. Although information about the regulation, survival program, and pathophysiological roles of Trm has been obtained from murine studies, little is known about the biology of human cutaneous Trm Here, we showed that host-derived CD69+ αβ memory T cell clones in the epidermis and dermis remain stable and functionally competent for at least 10 years in patients with allogeneic hematopoietic stem cell transplantation. Single-cell RNA sequencing revealed low expression of genes encoding tissue egress molecules by long-term persisting Trm in the skin, whereas tissue retention molecules and stem cell markers were displayed by Trm The transcription factor RUNX3 and the surface molecule galectin-3 were preferentially expressed by host T cells at the RNA and protein levels, suggesting two new markers for human skin Trm Furthermore, skin lesions from patients developing graft-versus-host disease (GVHD) showed a large number of cytokine-producing host-derived Trm, suggesting a contribution of these cells to the pathogenesis of GVHD. Together, our studies highlighted the relationship between the local human skin environment and long-term persisting Trm, which differs from murine skin. Our results also indicated that local tissue inflammation occurs through host-derived Trm after allogeneic hematopoietic stem cell transplantation.

A role for fibroblast growth factor receptor 1 in the pathogenesis of Neisseria meningitidis

Neisseria meningitidis (the meningococcus) remains an important cause of human disease, including meningitis and sepsis. Adaptation to the host environment includes many interactions with specific cell surface receptors, resulting in intracellular signalling and cytoskeletal rearrangements that contribute to pathogenesis. Here, we assessed the interactions between meningococci and Fibroblast Growth Factor Receptor 1-IIIc (FGFR1-IIIc): a receptor specific to endothelial cells of the microvasculature, including that of the blood-brain barrier. We show that the meningococcus recruits FGFR1-IIIc onto the surface of human blood microvascular endothelial cells (HBMECs). Furthermore, we demonstrate that expression of FGFR1-IIIc is required for optimal invasion of HBMECs by meningococci. We show that the ability of N. meningitidis to interact with the ligand-binding domain of FGFR1-IIIc is shared with the other pathogenic Neisseria species, N. gonorrhoeae, but not with commensal bacteria including non-pathogenic Neisseria 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.

The Effect of Influenza Virus on the Human Oropharyngeal Microbiome

Background

Secondary bacterial infections are an important cause of morbidity and mortality associated with influenza infections. As bacterial disease can be caused by a disturbance of the host microbiome, we examined the impact of influenza on the upper respiratory tract microbiome in a human challenge study.

Methods

The dynamics and ecology of the throat microbiome were examined following an experimental influenza challenge of 52 previously-healthy adult volunteers with influenza A/Wisconsin/67/2005 (H3N2) by intranasal inoculation; 35 healthy control subjects were not subjected to the viral challenge. Serial oropharyngeal samples were taken over a 30-day period, and the V1-V3 region of the bacterial 16S ribosomal RNA sequences were amplified and sequenced to determine the composition of the microbiome. The carriage of pathogens was also detected.

Results

Of the 52 challenged individuals, 43 developed proven influenza infections, 33 of whom became symptomatic. None of the controls developed influenza, although 22% reported symptoms. The diversity of bacterial communities remained remarkably stable following the acquisition of influenza, with no significant differences over time between individuals with influenza and those in the control group. Influenza infection was not associated with perturbation of the microbiome at the level of phylum or genus. There was no change in colonization rates with Streptococcus pneumoniae or Neisseria meningitidis.

Conclusions

The throat microbiota is resilient to influenza infection, indicating the robustness of the upper-airway microbiome.

Characterization and functional study of Galectin3 from Japanese flounder (Paralichthys olivaceus)

Galectins belong to the β-galactoside binding protein family and participate in both innate and acquired immunity. In this study, we described the molecular characteristics of Galectin3 gene from Japanese flounder (Paralichthys olivaceus), designed as PoGalectin3. Its open reading frame was 1128 bp, encoding a protein composed of 375 amino acids. PoGalectin3 belongs to chimeric galactose agglutinin, which contains a C-terminal carbohydrate recognition domain (CRD) (L₂₅₀-P₃₇₂), and its N-terminal is rich in proline (P) and glycine (G). Multiple sequence alignment and phylogenetic tree showed that PoGalectin3 was conservative in different aquatic animals. Tissue distribution confirmed that PoGalectin3 showed significantly highest expression in brain, moderate expression in liver, intestine and muscle. PoGalectin3 was significantly increased post infection with Edwardsiella tarda from intestine tissue of P. olivaceus. In order to investigate the binding ability of PoGalectin3 to pathogen-associated molecular patterns, the recombinant PoGalectin3 protein (rPoGalectin3) was successfully expressed and purified, and an Enzyme linked immunosorbent assay (ELISA) experiment was performed. ELISA refers to the qualitative and quantitative detection method of immune response by combining soluble antigen or antibody with solid-phase carrier. It was confirmed that rPoGalectin3 exhibited high affinity to lipopolysaccharide and peptidoglycan. The rPoGalectin3 also exhibited a concentration dependent binding capacity with Gram-positive bacteria (Bacillus pumilus, Bacillus subtilis, Bacillus cereus) and Gram-negative bacteria (Aeromonas salmonicida, E. tarda, Vibrio vulnificus). In addition, the results of microbial agglutination experiment showed that rPoGalectin3 could agglutinate Gram-positive bacteria (B. pumilus, B. subtilis) and Gram-negative bacteria (A. salmonicida, E. tarda) in the presence of Ca²⁺. In conclusion, this research laid an important foundation for the specific function analysis of PoGalectin3, which provide theoretical basis for the prevention and control of aquatic diseases.

The Examination of Viral Characteristics of HIV-1 CRF07_BC and Its Potential Interaction with Extracellular Galectin-3

HIV-1 CRF07_BC is a B’ and C subtype recombinant emerging virus and many of its viral characteristics remain unclear. Galectin-3 (Gal3) is a β-galactose binding lectin that has been reported as a pattern recognition receptor (PRR) and is known to mediate adhesion between cells and microbes. This study aims to examine the viral characteristics of HIV-1 CRF07_BC virus and the role of extracellular galectin-3 in HIV-1 CRF07_BC infection. A total of 28 HIV-1+ injecting drug users (IDUs) were recruited and 24 (85.7%) were identified as HIV-1 CRF07_BC. Results indicate that significant higher serum galectin-3 was measured in CRF07_BC infected patients and CRF07_BC infection triggered significant galectin-3 expression (p < 0.01). Viral characteristics demonstrate that CRF07_BC virions display a higher level of envelope gp120 spikes. The virus infectivity assay demonstrated that co-treatment with galectin-3 significantly promoted CRF07_BC attachment and internalization (p < 0.01). A co-immunoprecipitation assay showed that pulldown galectin-3 co-precipitated both CD4 and gp120 proteins. Results from an enzyme-linked immunosorbent assay (ELISA) indicate that the galectin-3 promoting effect occurs through enhancement of the interaction between gp120 and CD4. This study suggests that CRF07_BC was predominant in HIV-1+ IDUs and CRF07_BC utilized extracellular galectin-3 to enhance its infectivity via stabilization of the gp120-CD4 interaction.

Bacterial glycans and their interactions with lectins in the innate immune system

Bacterial surfaces are rich in glycoconjugates that are mainly present in their outer layers and are of great importance for their interaction with the host innate immune system. The innate immune system is the first barrier against infection and recognizes pathogens via conserved pattern recognition receptors (PRRs). Lectins expressed by innate immune cells represent an important class of PRRs characterized by their ability to recognize carbohydrates. Among lectins in innate immunity, there are three major classes including the galectins, siglecs, and C-type lectin receptors. These lectins may contribute to initial recognition of bacterial glycans, thus providing an early defence mechanism against bacterial infections, but they may also be exploited by bacteria to escape immune responses. In this review, we will first exemplify bacterial glycosylation systems; we will then describe modes of recognition of bacterial glycans by lectins in innate immunity and, finally, we will briefly highlight how bacteria have found ways to exploit these interactions to evade immune recognition.

Intracellular Galectin-9 Controls Dendritic Cell Function by Maintaining Plasma Membrane Rigidity

Endogenous extracellular Galectins constitute a novel mechanism of membrane protein organization at the cell surface. Although Galectins are also highly expressed intracellularly, their cytosolic functions are poorly understood. Here, we investigated the role of Galectin-9 in dendritic cell (DC) surface organization and function. By combining functional, super-resolution and atomic force microscopy experiments to analyze membrane stiffness, we identified intracellular Galectin-9 to be indispensable for plasma membrane integrity and structure in DCs. Galectin-9 knockdown studies revealed intracellular Galectin-9 to directly control cortical membrane structure by modulating Rac1 activity, providing the underlying mechanism of Galectin-9-dependent actin cytoskeleton organization. Consequent to its role in maintaining plasma membrane structure, phagocytosis studies revealed that Galectin-9 was essential for C-type-lectin receptor-mediated pathogen uptake by DCs. This was confirmed by the impaired phagocytic capacity of Galectin-9-null murine DCs. Together, this study demonstrates a novel role for intracellular Galectin-9 in modulating DC function, which may be evolutionarily conserved.

Interaction of host and Staphylococcus aureus protease-system regulates virulence and pathogenicity

Staphylococcus aureus causes various health care- and community-associated infections as well as certain chronic TH2 driven inflammatory diseases. It is a potent pathogen with serious virulence and associated high morbidity. Severe pathogenicity is accredited to the S. aureus secreted virulence factors such as proteases and host protease modulators. These virulence factors promote adhesion and invasion of bacteria through damage of tight junction barrier and keratinocytes. They inhibit activation and transmigration of various immune cells such as neutrophils (and neutrophil proteases) to evade opsono-phagocytosis and intracellular bacterial killing. Additionally, they protect the bacteria from extracellular killing by disrupting integrity of extracellular matrix. Platelet activation and agglutination is also impaired by these factors. They also block the classical as well as alternative pathways of complement activation and assist in spread of infection through blood and tissue. As these factors are exquisite factors of S. aureus mediated disease development, we have focused on review of diversification of various protease-system associated virulence factors, their structural building, diverse role in disease development and available therapeutic counter measures. This review summarises the role of protease-associated virulence factors during invasion and progression of disease.

Group A Streptococcus-Mediated Host Cell Signaling

In the past decade, the field of the cellular microbiology of group A Streptococcus (S. pyogenes) infection has made tremendous advances and touched upon several important aspects of pathogenesis, including receptor biology, invasive and evasive phenomena, inflammasome activation, strain-specific autophagic bacterial killing, and virulence factor-mediated programmed cell death. The noteworthy aspect of S. pyogenes-mediated cell signaling is the recognition of the role of M protein in a variety of signaling events, starting with the targeting of specific receptors on the cell surface and on through the induction and evasion of NETosis, inflammasome, and autophagy/xenophagy to pyroptosis and apoptosis. Variations in reports on S. pyogenes-mediated signaling events highlight the complex mechanism of pathogenesis and underscore the importance of the host cell and S. pyogenes strain specificity, as well as in vitro/in vivo experimental parameters. The severity of S. pyogenes infection is, therefore, dependent on the virulence gene expression repertoire in the host environment and on host-specific dynamic signaling events in response to infection. Commonly known as an extracellular pathogen, S. pyogenes finds host macrophages as safe havens wherein it survives and even multiplies. The fact that endothelial cells are inherently deficient in autophagic machinery compared to epithelial cells and macrophages underscores the invasive nature of S. pyogenes and its ability to cause severe systemic diseases. S. pyogenes is still one of the top 10 causes of infectious mortality. Understanding the orchestration of dynamic host signaling networks will provide a better understanding of the increasingly complex mechanism of S. pyogenes diseases and novel ways of therapeutically intervening to thwart severe and often fatal infections.

Expression profiling and functional characterization of galectin-3 of turbot (Scophthalmus maximus L.) in host mucosal immunity

Galectins, a family of evolutionary conserved β-galactoside-binding proteins, have been characterized in a wide range of species. Galectin-3 is the only member in the chimera type, which is a monomeric lectin with one CRD domain. A growing body of evidence have indicated vital roles of galectin-3 in innate immune responses against infection. Here, one galectin-3 gene was captured in turbot (SmLgals3) with a 1203 bp open reading frame (ORF). In comparison to other species, SmLgals3 showed the highest similarity and identity to large yellow croaker and medaka, respectively. The genomic structure analysis showed that SmLgals3 had 5 exons similar to other vertebrate species. The syntenic analysis revealed that galectin-3 had the same neighboring genes across all the selected species, which suggested the synteny encompassing galectin-3 region during vertebrate evolution. Subsequently, SmLgals3 was widely expressed in all the examined tissues, with the highest expression level in brain and the lowest expression level in skin. In addition, SmLgals3 was significantly down-regulated in intestine following both Gram-negative bacteria Vibrio anguillarum, and Gram-positive bacteria Streptococcus iniae immersion challenge. Finally, the rSmLgals3 showed strong binding ability to all the examined microbial ligands. Taken together, our results suggested SmLgals3 played vital roles in fish innate immune responses against infection. However, the knowledge of SmLgals3 are still limited in teleost species, further studies should be carried out to better characterize its detailed roles in teleost mucosal immunity.

Extracellular galectin-1 enhances adhesion to and invasion of oral epithelial cells by Porphyromonas gingivalis

Galectin-1 and galectin-3 are C-type lectin receptors that bind to lipopolysaccharide in the cell wall of gram-negative bacteria. In this study, we investigated the effects of galectin-1 and galectin-3 on adhesion to and invasion of the human gingival epithelial cell line Ca9-22 by Porphyromonas gingivalis, a periodontal pathogenic gram-negative bacterium. Recombinant galectin-1, but not galectin-3, enhanced P. gingivalis adhesion and invasion, although both galectins bound similarly to P. gingivalis. Flow cytometry also revealed that Ca9-22 cells express low levels of galectin-1 and moderate levels of galectin-3. Ca9-22 cells in which galectin-3 was knocked-down did not exhibit enhanced P. gingivalis adhesion and invasion. Similarly, specific antibodies to galectin-1 and galectin-3 did not inhibit P. gingivalis adhesion and invasion. These results suggest that soluble galectin-1, but not galectin-3, may exacerbate periodontal disease by enhancing the adhesion to and invasion of host cells by periodontal pathogenic bacteria.

Identification of targets of IL-13 and STAT6 signaling in polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a life-threatening, highly prevalent monogenic disease caused by mutations in polycystin-1 (PC1) in 85% of patients. We have previously identified a COOH-terminal cleavage fragment of PC1, PC1-p30, which interacts with the transcription factor STAT6 to promote transcription. STAT6 is aberrantly active in PKD mouse models and human ADPKD, and genetic removal or pharmacological inhibition of STAT6 attenuates disease progression. High levels of IL-13, a STAT6-activating cytokine, are found in the cyst fluid of PKD mouse models and increased IL-13 receptors in ADPKD patient tissue, suggesting that a positive feedback loop exists between IL-13 and STAT6 is activated in cystic epithelial cells and contributes to disease progression. In this study, we aimed to identify genes aberrantly regulated by STAT6 to better understand how increased IL-13/STAT6 signaling may contribute to PKD progression. We demonstrate that the expression of periostin, galectin-3, and IL-24 is upregulated in various forms of PKD and that their aberrant regulation is mediated by IL-13 and STAT6 activity. Periostin and galectin-3 have previously been implicated in PKD progression. We support these findings by showing that periostin expression is increased after IL-13 treatment in kidney epithelial cells, that galectin-3 expression is increased after injecting IL-13 in vivo and that IL-24 expression is upregulated by both IL-13 treatment and PC1-p30 overexpression in mouse and human kidney cells. Overall, these findings provide insight into the possible mechanisms by which increased IL-13/STAT6 signaling contributes to PKD progression and suggest potential therapeutic targets.

Galectin-3 Plays an Important Role in Preterm Birth Caused by Dental Infection of Porphyromonas gingivalis

Dental infection is risk for preterm birth (PTB) through unclear mechanisms. We established a dental infection-induced PTB mouse model, in which Porphyromonas gingivalis (P.g.) induced PTB by 2 days. We analysed pathogenic factors contributing to PTB and their effects on trophoblasts in vitro. TNF-α, IL-8, and COX-2 were upregulated in P.g.-infected placenta. Galectin-3 (Gal-3), an immune regulator, was significantly upregulated in placenta, amniotic fluid, and serum. In vitro, P.g.-lipopolysaccharide (P.g.-LPS) increased TNF-α and Gal-3 in trophoblasts via NF-κB/MAPK signalling. Gal-3 inhibition significantly downregulated P.g.-LPS-induced TNF-α production. TNF-α upregulated Gal-3. Gal-3 also increased cytokines and Gal-3 through NF-κB/MAPK signalling. Moreover, Gal-3 suppressed CD-66a expression at the maternal-foetal interface. Co-stimulation with Gal-3 and P.g.-LPS upregulated cytokine levels, while Gal-3 plus Aggregatibacter actinomycetemcomitans (A.a.)- or Escherichia coli (E. coli)-LPS treatment downregulated them, indicating the critical role of Gal-3 especially in P.g. dental infection-induced PTB. P.g.-dental infection induced PTB, which was associated with Gal-3-dependent cytokine production. New therapies and/or diagnostic systems targeting Gal-3 may reduce PTB.

Macromolecular assemblies of complex polysaccharides with galectin-3 and their synergistic effects on function

Although pectin-derived polysaccharides can antagonize galectin function in various pathological disorders, the nature of their binding interactions needs to be better defined for developing them as drugs. Moreover, given their relatively large size and complexity, pectin-derived polysaccharides are also useful as model systems to assess inter-polysaccharide and protein-polysaccharide interactions. Here, we investigated interactions between galectin-3 (Gal-3) and pectin-derived polysaccharides: a rhamnogalacturonan (RG) and two homogalacturonans (HGs). BioLayer Interferometry and fluorescence-linked immunosorbent assays indicate that these polysaccharides bind Gal-3 with macroscopic or apparent K_D values of 49 nM, 46 µM, and 138 µM, respectively. ¹⁵N-¹H heteronuclear single quantum coherence (HSQC) NMR studies reveal that these polysaccharides interact primarily with the F-face of the Gal-3 carbohydrate recognition domain. Even though their binding to Gal-3 does not inhibit Gal-3-mediated T-cell apoptosis and only weakly attenuates hemagglutination, their combination in specific proportions increases activity synergistically along with avidity for Gal-3. This suggests that RG and HG polysaccharides act in concert, a proposal supported by polysaccharide particle size measurements and ¹³C-¹H HSQC data. Our model has HG interacting with RG to promote increased avidity of RG for Gal-3, likely by exposing additional lectin-binding sites on the RG. Overall, the present study contributes to our understanding of how complex HG and RG polysaccharides interact with Gal-3.

Key regulators of galectin-glycan interactions

Protein-ligand interactions serve as fundamental regulators of numerous biological processes. Among protein-ligand pairs, glycan binding proteins (GBPs) and the glycans they recognize represent unique and highly complex interactions implicated in a broad range of regulatory activities. With few exceptions, cell surface receptors and secreted proteins are heavily glycosylated. As these glycans often represent highly regulatable post-translational modifications, alterations in glycosylation can fundamentally impact GBP recognition. Among GBPs, galectins in particular appear to engage a diverse set of glycan determinants to impact a broad range of biological processes. In this review, we will explore factors that impact galectin activity, including the effect of glycan modification on galectin-glycan interactions.

Galectin-3 Inhibits Galectin-8/Parkin-Mediated Ubiquitination of Group A Streptococcus

Group A streptococcus (GAS) is an important human pathogen that causes a wide variety of cutaneous and systemic infections. Although originally thought to be an extracellular bacterium, numerous studies have demonstrated that GAS can trigger internalization into nonimmune cells to escape from immune surveillance or antibiotic-mediated killing. Epithelial cells possess a defense mechanism involving autophagy-mediated targeting and killing of GAS within lysosome-fused autophagosomes. In endothelial cells, in contrast, we previously showed that autophagy is not sufficient for GAS killing. In the present study, we showed higher galectin-3 (Gal-3) expression and lower Gal-8 expression in endothelial cells than in epithelial cells. The recruitment of Gal-3 to GAS is higher and the recruitment of Gal-8 to GAS is lower in endothelial cells than in epithelial cells. We further showed that Gal-3 promotes GAS replication and diminishes the recruitment of Gal-8 and ubiquitin, the latter of which is a critical protein for autophagy sequestration. After knockdown of Gal-3 in endothelial cells, the colocalization of Gal-8, parkin, and ubiquitin-decorated GAS is significantly increased, as is the interaction of Gal-8 and parkin, an E3 ligase. Furthermore, inhibition of Gal-8 in epithelial cells attenuates recruitment of parkin; both Gal-8 and parkin contribute to ubiquitin recruitment and GAS elimination. Animal studies confirmed that Gal-3-knockout mice develop less-severe skin damage and that GAS replication can be detected only in the air pouch and not in organs and endothelial cells. These results demonstrate that Gal-3 inhibits ubiquitin recruitment by blocking Gal-8 and parkin recruitment, resulting in GAS replication in endothelial cells.

In epithelial cells, GAS can be efficiently killed within the lysosome-fused autophaosome compartment. However, we previously showed that, in spite of LC-3 recruitment, the autophagic machinery is not sufficient for GAS killing in endothelial cells. In this report, we provide the first evidence that Gal-3, highly expressed in endothelial cells, blocks the tagging of ubiquitin to GAS by inhibiting recruitment of Gal-8 and parkin, leading to an enhancement of GAS replication. We also provide the first demonstration that Gal-8 can interact with parkin, the critical E3 ligase, for resistance to intracellular bacteria by facilitating the decoration of bacteria with ubiquitin chains. Our findings reveal that differential levels of Gal-3 and Gal-8 expression and recruitment to GAS between epithelial cells and endothelial cells may contribute to the different outcomes of GAS elimination or survival and growth of GAS in these two types of cells.

Galectin-3 Is a Target for Proteases Involved in the Virulence of Staphylococcus aureus

Staphylococcus aureus is a major cause of skin and soft tissue infection. The bacterium expresses four major proteases that are emerging as virulence factors: aureolysin (Aur), V8 protease (SspA), staphopain A (ScpA), and staphopain B (SspB). We hypothesized that human galectin-3, a β-galactoside-binding lectin involved in immune regulation and antimicrobial defense, is a target for these proteases and that proteolysis of galectin-3 is a novel immune evasion mechanism. Indeed, supernatants from laboratory strains and clinical isolates of S. aureus caused galectin-3 degradation. Similar proteolytic capacities were found in Staphylococcus epidermidis isolates but not in Staphylococcus saprophyticus Galectin-3-induced activation of the neutrophil NADPH oxidase was abrogated by bacterium-derived proteolysis of galectin-3, and SspB was identified as the major protease responsible. The impact of galectin-3 and protease expression on S. aureus virulence was studied in a murine skin infection model. In galectin-3^+/+ mice, SspB-expressing S. aureus caused larger lesions and resulted in higher bacterial loads than protease-lacking bacteria. No such difference in bacterial load or lesion size was detected in galectin-3^-/- mice, which overall showed smaller lesion sizes than the galectin-3^+/+ animals. In conclusion, the staphylococcal protease SspB inactivates galectin-3, abrogating its stimulation of oxygen radical production in human neutrophils and increasing tissue damage during skin infection.

The Many Roles of Galectin-3, a Multifaceted Molecule, in Innate Immune Responses against Pathogens

Galectins are a group of evolutionarily conserved proteins with the ability to bind β-galactosides through characteristic carbohydrate-recognition domains (CRD). Galectin-3 is structurally unique among all galectins as it contains a C-terminal CRD linked to an N-terminal protein-binding domain, being the only chimeric galectin. Galectin-3 participates in many functions, both intra- and extracellularly. Among them, a prominent role for Galectin-3 in inflammation has been recognized. Galectin-3 has also been shown to directly bind to pathogens and to have various effects on the functions of the cells of the innate immune system. Thanks to these two properties, Galectin-3 participates in several ways in the innate immune response against invading pathogens. Galectin-3 has been proposed to function not only as a pattern-recognition receptor (PRR) but also as a danger-associated molecular pattern (DAMP). In this review, we analyze the various roles that have been assigned to Galectin-3, both as a PRR and as a DAMP, in the context of immune responses against pathogenic microorganisms.

Innate immune recognition and inflammation in Neisseria meningitidis infection

Neisseria meningitidis (Nme) can cause meningitis and sepsis, diseases which are characterised by an overwhelming inflammatory response. Inflammation is triggered by host pattern recognition receptors (PRRs) which are activated by pathogen-associated molecular patterns (PAMPs). Nme contains multiple PAMPs including lipooligosaccharide, peptidoglycan, proteins and metabolites. Various classes of PRRs including Toll-like receptors, NOD-like receptors, C-type lectins, scavenger receptors, pentraxins and others are expressed by the host to respond to any given microbe. While Toll-like receptors and NOD-like receptors are pivotal in triggering inflammation, other PRRs act as modulators of inflammation or aid in functional antimicrobial responses such as phagocytosis or complement activation. This review aims to give an overview of the various Nme PAMPs reported to date, the PRRs they activate and their implications during the inflammatory response to infection.

Innate immunity against molecular mimicry: Examining galectin-mediated antimicrobial activity

Adaptive immunity provides the unique ability to respond to a nearly infinite range of antigenic determinants. Given the inherent plasticity of the adaptive immune system, a series of tolerance mechanisms exist to reduce reactivity toward self. While this reduces the probability of autoimmunity, it also creates an important gap in adaptive immunity: the ability to recognize microbes that look like self. As a variety of microbes decorate themselves in self-like carbohydrate antigens and tolerance reduces the ability of adaptive immunity to react with self-like structures, protection against molecular mimicry likely resides within the innate arm of immunity. In this review, we will explore the potential consequences of microbial molecular mimicry, including factors within innate immunity that appear to specifically target microbes expressing self-like antigens, and therefore provide protection against molecular mimicry.

Ricin-B-lectin enhances microsporidia Nosema bombycis infection in BmN cells from silkworm Bombyx mori

Nosema bombycis is an obligate intracellular parasitic fungus that utilizes a distinctive mechanism to infect Bombyx mori Spore germination can be used for host cell invasion; however, the detailed mechanism remains to be elucidated. The ricin-B-lectin (RBL) gene is significantly differentially regulated after N. bombycis spore germination, and NbRBL might play roles in spore germination and infection. In this study, the biological function of NbRBL was examined. Protein sequence analysis showed that NbRBL is a secreted protein that attaches to carbohydrates. The relative expression level of the NbRBL gene was low during the first 30 h post-infection (hpi) in BmN cells, and high expression was detected from 42 hpi. Gene cloning, prokaryotic expression, and antibody preparation for NbRBL were performed. NbRBL was detected in total and secreted proteins using western blot analysis. Subcellular localization analysis showed that NbRBL is an intracellular protein. Spore adherence and infection assays showed that NbRBL could enhance spore adhesion to BmN cells; the proliferative activities of BmN cells incubated with anti-NbRBL were higher than those in negative control groups after N. bombycis infection; and the treatment groups showed less damage from spore invasion. We therefore, propose that NbRBL is released during spore germination, enhances spore adhesion to BmN cells, and contributes to spore invasion.

Disease and Carrier Isolates of Neisseria meningitidis Cause G1 Cell Cycle Arrest in Human Epithelial Cells

Microbial pathogens have developed several mechanisms to modulate and interfere with host cell cycle progression. In this study, we analyzed the effect of the human pathogen Neisseria meningitidis on the cell cycle of epithelial cells. Two pathogenic isolates, as well as two carrier isolates, were tested for their ability to adhere to and invade into the epithelial cell lines Detroit 562 and NP69 and to modulate the cell cycle. We found that all isolates adhered equally well to both Detroit 562 and NP69 cells, whereas the carrier isolates were significantly less invasive. Using propidium iodide staining and 5-ethynyl-2'-deoxyuridine pulse-labeling, we provide evidence that meningococcal infection arrested cells in the G1 phase of the cell cycle at 24 h postinfection. In parallel, a significant decrease of cells in the S phase was observed. Interestingly, G1-phase arrest was only induced after infection with live bacteria but not with heat-killed bacteria. By Western blotting we demonstrate that bacterial infection resulted in a decreased protein level of the cell cycle regulator cyclin D1, whereas cyclin E expression levels were increased. Furthermore, N. meningitidis infection induced an accumulation of the cyclin-dependent kinase inhibitor (CKI) p21(WAF1/CIP1) that was accompanied by a redistribution of this CKI to the cell nucleus, as shown by immunofluorescence analysis. Moreover, the p27(CIP1) CKI was redistributed and showed punctate foci in infected cells. In summary, we present data that N. meningitidis can interfere with the processes of host cell cycle regulation.

Galectin-3 binds highly galactosylated IgG1 and is crucial for the IgG1 complex mediated inhibition of C5aReceptor induced immune responses

Changes in the glycosylation of immunoglobulins have been shown to modulate immune homeostasis and disease pathology. In this sense it has been shown that highly galactosylated but not agalactosylated IgG1 immune complexes (ICs) inhibit C5aR-mediated pro-inflammatory immune responses via the assembly of FcγRIIB-Dectin-1 receptor complexes. In this study we demonstrated that Galectin-3, a galactose-binding lectin that is known to cross-link proteins on cell-surfaces via binding their N-glycans, bound to highly-galactosylated, but not agalactosylated IgG1. Further, Galectin-3 was essential for the IC-mediated inhibition of C5a-induced neutrophil chemotaxis in vitro. Taken together our results indicate that Galectin-3 mediates the interaction of ICs with the FcγRIIB-Dectin-1 receptor complex for delivering immunoregulatory signals to inhibit C5aR-mediated immune responses.

The Cek1‑mediated MAP kinase pathway regulates exposure of α‑1,2 and β‑1,2‑mannosides in the cell wall of Candida albicans modulating immune recognition

The Cek1 MAP kinase (MAPK) mediates vegetative growth and cell wall biogenesis in the fungal pathogen Candida albicans. Alterations in the fungal cell wall caused by a defective Cek1‑mediated signaling pathway leads to increased β‑1,3‑glucan exposure influencing dectin‑1 fungal recognition by immune cells. We show here that cek1 cells also display an increased exposure of α‑1,2 and β‑1,2‑mannosides (α‑M and β‑M), a phenotype shared by strains defective in the activating MAPKK Hst7, suggesting a general defect in cell wall assembly. cek1 cells display walls with loosely bound material as revealed by transmission electron microscopy and are sensitive to tunicamycin, an inhibitor of N‑glycosylation. Transcriptomal analysis of tunicamycin treated cells revealed a differential pattern between cek1 and wild type cells which involved mainly cell wall and stress related genes. Mapping α‑M and β‑M epitopes in the mannoproteins of different cell wall fractions (CWMP) revealed an important shift in the molecular weight of the mannan derived from mutants defective in this MAPK pathway. We have also assessed the role of galectin‑3, a member of a β‑galactoside‑binding protein family shown to bind to and kill C. albicans through β‑M recognition, in the infection caused by cek1 mutants. Increased binding of cek1 to murine macrophages was shown to be partially blocked by lactose. Galectin-3(-/-) mice showed increased resistance to fungal infection, although galectin-3 did not account for the reduced virulence of cek1 mutants in a mouse model of systemic infection. All these data support a role for the Cek1‑mediated pathway in fungal cell wall maintenance, virulence and antifungal discovery.

Galectin-3 suppresses mucosal inflammation and reduces disease severity in experimental colitis

Galectin-3, a member of the β-galactoside-binding lectin family, expresses in many different immune cells and modulates broad biological functions including cell adhesion, cell activation, cell growth, apoptosis, and inflammation. However, the role of galectin-3 in mucosal immunity or inflammatory bowel diseases is still not clear. We demonstrate here that galectin-3 knockout mice have more severe disease activity in the dextran sulfate sodium (DSS)-induced colitis model, indicating that galectin-3 may protect from inflammation in DSS-induced colitis. Furthermore, treating with galectin-3 reduced body weight loss, shortened colonic length, and ameliorated mucosal inflammation in mice having DSS-induced colitis. However, the protective effects of galectin-3 were eliminated by the administration of anti-CD25 mAb. In addition, primary T cells treated with galectin-3 ex vivo induced the expression of FOXP3, ICOS, and PD-1 with a Treg cell phenotype having a suppression function. Moreover, adoptive transfer of galectin-3-treated T cells reduced bowel inflammation and colitis in the T cell transfer colitis model. In conclusion, our results indicate that galectin-3 inhibited colonic mucosa inflammation and reduced disease severity by inducing regulatory T cells, suggesting that it is a potential therapeutic approach in inflammatory bowel disease.

KEY MESSAGES

Galectin-3 offers protection from inflammation in experimental colitis. Galectin-3 knockout mice have more severe disease activity in DSS-induced colitis. Adoptive transfer of galectin-3-treated T cells reduced bowel inflammation. Galectin-3 inhibited colonic mucosa inflammation by inducing regulatory T cells. Galectin-3 is a potential therapeutic approach in inflammatory bowel disease.

Galectin-3 In Obesity And Type 2 Diabetes

Galectin-3 is an important regulator of inflammation and acts as a receptor for advanced-glycation (AGE) and lipoxidation end-products (ALE). Evidence indicates a significant upregulation in circulating levels and visceral adipose tissue production of Galectin-3 in obesity and type 2 diabetes. Recent studies demonstrate development of obesity and dysregulation of glucose metabolism in Galectin-3 “knockout” (KO) mice, which also develop accelerated and more severe pathology in models of atherosclerosis and metabolically-induced kidney damage. Thus, evidence that Galectin-3 is an important player in metabolic disease is accumulating. This review discusses current evidence on the connection between Galectin-3 and metabolic disease, focusing on mechanisms by which this galectin modulates adiposity, glucose metabolism and obesity-associated inflammatory responses.

Galectin-8 promotes regulatory T-cell differentiation by modulating IL-2 and TGFβ signaling

Galectins have emerged as potent immunoregulatory molecules that control chronic inflammation through distinct mechanisms. Galectin-8 (Gal-8), a tandem-repeat type galectin with unique preference for α2,3-sialylated glycans, is ubiquitously expressed, but little is known about its role in T cell differentiation. Here, we report that Gal-8 promotes the polyclonal differentiation of primary mouse Treg cells in vitro. We further show that Gal-8 also facilitates antigen-specific differentiation of regulatory T (Treg) cells, and that Treg cells polarized in the presence of Gal-8 express cytotoxic T lymphocyte antigen-4 (CTLA-4) and IL-10 at a higher frequency than control Treg cells, and efficiently inhibit proliferation of activated T cells in vitro. Investigation of the mechanism by which Gal-8 promotes Treg conversion revealed that Gal-8 activates TGFβ signaling and promotes sustained IL-2R signaling. Taken together, these data suggest that Gal-8 promotes the differentiation of highly suppressive Treg cells, which has implications for the treatment of inflammatory and autoimmune diseases.

Deciphering the complex three-way interaction between the non-integrin laminin receptor, galectin-3 and Neisseria meningitidis

The non-integrin laminin receptor (LAMR1/RPSA) and galectin-3 (Gal-3) are multi-functional host molecules with roles in diverse pathological processes, particularly of infectious or oncogenic origins. Using bimolecular fluorescence complementation and confocal imaging, we demonstrate that the two proteins homo- and heterodimerize, and that each isotype forms a distinct cell surface population. We present evidence that the 37 kDa form of LAMR1 (37LRP) is the precursor of the previously described 67 kDa laminin receptor (67LR), whereas the heterodimer represents an entity that is distinct from this molecule. Site-directed mutagenesis confirmed that the single cysteine (C(173)) of Gal-3 or lysine (K(166)) of LAMR1 are critical for heterodimerization. Recombinant Gal-3, expressed in normally Gal-3-deficient N2a cells, dimerized with endogenous LAMR1 and led to a significantly increased number of internalized bacteria (Neisseria meningitidis), confirming the role of Gal-3 in bacterial invasion. Contact-dependent cross-linking determined that, in common with LAMR1, Gal-3 binds the meningococcal secretin PilQ, in addition to the major pilin PilE. This study adds significant new mechanistic insights into the bacterial-host cell interaction by clarifying the nature, role and bacterial ligands of LAMR1 and Gal-3 isotypes during colonization.