Galectin-1 Modulates the Fusogenic Activity of Placental Endogenous Retroviral Envelopes.

Syncytin-1 and -2 are glycoproteins encoded by human endogenous retrovirus (hERV) that, through their fusogenic properties, are needed for the formation of the placental syncytiotrophoblast. Previous studies suggested that these proteins, in addition to the EnvP(b) envelope protein, are also involved in other cell fusion events. Since galectin-1 is a ß-galactoside-binding protein associated with cytotrophoblast fusion during placental development, we previously tested its effect on Syncytin-mediated cell fusion and showed that this protein differently modulates the fusogenic potential of Syncytin-1 and -2. Herein, we were interested in comparing the impact of galectin-1 on hERV envelope proteins in different cellular contexts. Using a syncytium assay, we first demonstrated that galectin-1 increased the fusion of Syncytin-2- and EnvP(b)-expressing cells. We then tested the infectivity of Syncytin-1 and -2 vs. VSV-G-pseudotyped viruses toward Cos-7 and various human cell lines. In the presence of galectin-1, infection of Syncytin-2-pseudotyped viruses augmented for all cell lines. In contrast, the impact of galectin-1 on the infectivity of Syncytin-1-pseudotyped viruses varied, being cell- and dose-dependent. In this study, we report the functional associations between three hERV envelope proteins and galectin-1, which should provide information on the fusogenic activity of these proteins in the placenta and other biological and pathological processes.

Galectin-3 enhances neutrophil motility and extravasation into the airways during Aspergillus fumigatus infection.

Aspergillus fumigatus is an opportunistic mold that infects patients who are immunocompromised or have chronic lung disease, causing significant morbidity and mortality in these populations. While the factors governing the host response to A. fumigatus remain poorly defined, neutrophil recruitment to the site of infection is critical to clear the fungus. Galectin-3 is a mammalian ß-galactose-binding lectin with both antimicrobial and immunomodulatory activities, however the role of galectin-3 in the defense against molds has not been studied. Here we show that galectin-3 expression is markedly up-regulated in mice and humans with pulmonary aspergillosis. Galectin-3 deficient mice displayed increased fungal burden and higher mortality during pulmonary infection. In contrast to previous reports with pathogenic yeast, galectin-3 exhibited no antifungal activity against A. fumigatus in vitro. Galectin-3 deficient mice exhibited fewer neutrophils in their airways during infection, despite normal numbers of total lung neutrophils. Intravital imaging studies confirmed that galectin-3 was required for normal neutrophil migration to the airspaces during fungal infection. Adoptive transfer experiments demonstrated that stromal rather than neutrophil-intrinsic galectin-3 was necessary for normal neutrophil entry into the airspaces. Live cell imaging studies revealed that extracellular galectin-3 directly increases neutrophil motility. Taken together, these data demonstrate that extracellular galectin-3 facilitates recruitment of neutrophils to the site of A. fumigatus infection, and reveals a novel role for galectin-3 in host defense against fungal infections.

Metazoan Soluble ß-Galactoside-Binding Lectins, Galectins: Methods for Purification, Characterization of Their Carbohydrate-Binding Specificity, and Probing Their Ligands.

Galectins are a family of soluble ß-galactoside-binding proteins that share conserved carbohydrate recognition domain. Galectins are found in most multicellular organisms and exert various biological functions by binding to the surface glycoconjugates as lectins. In this chapter, we describe the general methods of purification of galectins, quality control of purified galectins, some example methods of evaluating their carbohydrate-binding activity, and use of galectin to search or detect galectin ligands as well as a series of precautions for the usage of galectins.

Galectin-1 interacts with the human endogenous retroviral envelope protein syncytin-2 and potentiates trophoblast fusion in humans.

Syncytin (Syn)-2 is an important fusogenic protein that contributes to the formation of the placental syncytiotrophoblast. Galectin (Gal)-1, a soluble lectin, is also involved in trophoblast cell fusion and modulates the interaction of certain retroviral envelopes with their cellular receptor. This study aimed to investigate the association between Syn-2 and Gal-1 during human trophoblast cell fusion. This association was evaluated in vitro on primary villous cytotrophoblasts (vCTBs) and cell lines using recombinant Gal-1 and Syn-2-pseudotyped viruses. Using lactose, a Gal antagonist, and Gal-1-specific small interfering RNA (siRNA) transfections, we confirmed the implication of Gal-1 in vCTBs and BeWo cell fusion, although RT-PCR and ELISA analyses suggested that Gal-1 alone did not induce syncytialization. Infection assays showed a specific and significant effect of Gal-1 on the infectivity of Syn-2-pseudotyped viruses that depended on the expression of major facilitator superfamily domain-containing 2A (MFSD2a). Moreover, Gal-3, another placental Gal, did not modulate the infectivity of Syn-2-positive viruses, strengthening the specific association between Gal-1 and Syn-2. Interestingly, Gal-1 significantly reduced the infectivity of Syn-1-pseudotyped viruses, suggesting the opposite effects of Gal-1 on Syn-1 and -2. Finally, coimmunoprecipitation experiments showed a glycan-dependent interaction between Syn-2-bearing virions and Gal-1. We conclude that Gal-1 specifically interacts with Syn-2 and possibly regulates Syn-2/MFSD2a interaction during syncytialization of trophoblastic cells.-Toudic, C., Vargas, A., Xiao, Y., St-Pierre, G., Bannert, N., Lafond, J., Rassart, É., Sato, S., Barbeau, B. Galectin-1 interacts with the human endogenous retroviral envelope protein syncytin-2 and potentiates trophoblast fusion in humans.

What the Cardiologist Should Know About Mitochondrial Cardiomyopathy?

Mitochondrial diseases are a heterogeneous group of rare hereditary disorders that may manifest with single organ involvement or as multisystemic disease. The pathophysiology of mitochondrial disease is complex and related to mutations of genes encoding mitochondrial proteins that are crucial to the cellular respiratory chain. Given its almost exclusive aerobic metabolism, the heart is particularly susceptible to mitochondrial dysfunction and commonly involved in mitochondrial disorders. Various clinical presentations are described, making clinical recognition challenging. Some patients may evolve towards the early need for heart transplantation, which emphasizes the importance of appropriate diagnosis and referral to a specialized centre.

Galectin-3 and N-acetylglucosamine promote myogenesis and improve skeletal muscle function in the mdx model of Duchenne muscular dystrophy.

The muscle membrane, sarcolemma, must be firmly attached to the basal lamina. The failure of proper attachment results in muscle injury, which is the underlying cause of Duchenne muscular dystrophy (DMD), in which mutations in the dystrophin gene disrupts the firm adhesion. In patients with DMD, even moderate contraction causes damage, leading to progressive muscle degeneration. The damaged muscles are repaired through myogenesis. Consequently, myogenesis is highly active in patients with DMD, and the repeated activation of myogenesis leads to the exhaustion of the myogenic stem cells. Therefore, approaches to reducing the risk of the exhaustion are to develop a treatment that strengthens the interaction between the sarcolemma and the basal lamina and increases the efficiency of the myogenesis. Galectin-3 is an oligosaccharide-binding protein and is known to be involved in cell-cell interactions and cell-matrix interactions. Galectin-3 is expressed in myoblasts and skeletal muscle, although its function in muscle remains elusive. In this study, we found evidence that galectin-3 and the monosaccharide N-acetylglucosamine, which increases the synthesis of binding partners (oligosaccharides) of galectin-3, promote myogenesis in vitro. Moreover, in the mdx mouse model of DMD, treatment with N-acetylglucosamine increased muscle-force production. The results suggest that treatment with N-acetylglucosamine might mitigate the burden of DMD.-Rancourt, A., Dufresne, S. S., St-Pierre, G., Lévesque, J.-C., Nakamura, H., Kikuchi, Y., Satoh, M. S., Frenette, J., Sato, S. Galectin-3 and N-acetylglucosamine promote myogenesis and improve skeletal muscle function in the mdx model of Duchenne muscular dystrophy.

Trichomonas vaginalis Lipophosphoglycan Exploits Binding to Galectin-1 and -3 to Modulate Epithelial Immunity.

Trichomoniasis is the most common non-viral sexually transmitted infection caused by the vaginotropic extracellular protozoan parasite Trichomonas vaginalis. The infection is recurrent, with no lasting immunity, often asymptomatic, and linked to pregnancy complications and risk of viral infection. The molecular mechanisms of immune evasion by the parasite are poorly understood. We demonstrate that galectin-1 and -3 are expressed by the human cervical and vaginal epithelial cells and act as pathogen-recognition receptors for the ceramide phosphoinositol glycan core (CPI-GC) of the dominant surface protozoan lipophosphoglycan (LPG). We used an in vitro model with siRNA galectin knockdown epithelial clones, recombinant galectins, clinical Trichomonas isolates, and mutant protozoan derivatives to dissect the function of galectin-1 and -3 in the context of Trichomonas infection. Galectin-1 suppressed chemokines that facilitate recruitment of phagocytes, which can eliminate extracellular protozoa (IL-8) or bridge innate to adaptive immunity (MIP-3α and RANTES (regulated on activation normal T cell expressed and secreted)). Silencing galectin-1 increased and adding exogenous galectin-1 suppressed chemokine responses to Trichomonas or CPI-GC/LPG. In contrast, silencing galectin-3 reduced IL-8 response to LPG. Live Trichomonas depleted the extracellular levels of galectin-3. Clinical isolates and mutant Trichomonas CPI-GC that had reduced affinity to galectin-3 but maintained affinity to galectin-1 suppressed chemokine expression. Thus via CPI-GC binding, Trichomonas is capable of regulating galectin bioavailability and function to the benefit of its parasitic survival. These findings suggest novel approaches to control trichomoniasis and warrant further studies of galectin-binding diversity among clinical isolates as a possible source for symptom disparity in parasitic infections.

Role of galectin-3 in the initial control of Leishmania infection.

Galectin-3 belongs to a family of galectins, evolutionarily conserved glycan binding proteins (lectins) that have recently attracted much attention as modulators in adaptive immune responses. Previously, galectins have been considered lectins that bind only to endogenous "self" glycans. Further, galectins are synthesized and stored in the cytosol, where there are virtually no glycan-containing proteins, raising doubts over the biological significance of their glycan binding capacity. As discussed in this review, with particular emphasis on the role of galectin-3 in the innate immune response against the protozoan parasite Leishmania, several recent studies have suggested that galectin-3 could recognize L. major-specific pathogen-associated molecular pattern and, in parallel, facilitate the infiltration of neutrophils to the infected sites that helps reduce the initial parasite burden once galectin-3 is released as a damage-associated molecular pattern. Thus, while further investigation is necessary, based on the current results, it could be proposed that galectin-3 can hinge two areas of the innate immune recognition system, DAMP and PAMP pathways in the early host responses against various pathogens.

Galectin-3 facilitates neutrophil recruitment as an innate immune response to a parasitic protozoa cutaneous infection.

When infection occurs, neutrophils rapidly migrate to the affected site. Although the neutrophils neutralize microorganisms, they can also cause tissue damage or render invasion pathways to pathogens. Thus, the migration could be either beneficial or unfavorable in the initial control of infection. Studies on neutrophil recruitment revealed its complexity, especially in terms of the regulation of its initiation. Galectin-3 is a member of the galectin family that has an affinity for ß-galactoside containing glycoconjugates. In this study, we investigated the role of galectin-3 in neutrophil migration and the biological significance of the rapid migration of neutrophils in an experimental parasitic cutaneous infection with Leishmania major. When the substrain of L. major, LV39, was infected, lack of galectin-3 impaired neutrophil recruitment in the footpads and the draining lymph nodes 1 d following infection. Reduced number of recruited neutrophils correlated with local high parasite burdens. In contrast, neutrophil migration, induced by the other L. major substrain, Friedlin, was unaffected, and the initial parasite burden remained similar in galectin-3 null mice as compared with wild-type mice. Infection with L. major LV39 but not Friedlin induced higher levels of extracellular release of galectin-3. Further, galectin-3 alone was able to initiate neutrophil migration even though galectin-3 is not a chemoattractant for neutrophils. Thus, our data suggest that once extracellularly released, galectin-3 can act as a damage-associated molecular pattern to facilitate early neutrophil migration, which is beneficial in the initial control of the Leishmania infection.