Sialic acid-binding lectins (SABLs) from Solen grandis function as PRRs ensuring immune recognition and bacterial clearance

Molecular identification and functional analysis of MyD88 in giant freshwater prawn (Macrobrachium rosenbergii) and expression changes in response to bacterial challenge

Myeloid differentiation factor 88 (MyD88) is a crucial adaptor protein for Toll-like receptor (TLR)-mediated signaling pathways and plays an important role in immune response. In this study, the full-length cDNA of MyD88 from Macrobrachium rosenbergii (MRMyD88) was cloned. The MRMyD88 cDNA is 1758 bp long and contains a 1398-bp open reading frame. Multiple sequence alignment and phylogenetic analysis revealed that the amino acid sequence of MRMyD88 shared high identity with the known MyD88 proteins. The MRMyD88 mRNA was widely expressed in all examined tissues, with highest level in intestine, followed by gonad and pleopod. Furthermore, the MRMyD88 promoter region, spanning 1622 bp, contains several transcription factor-binding sites, including nine GATA-1 box motifs. Electrophoretic mobility shift assay showed that Gfi-1, SRF, and Oct-1 bind to the upstream region of MRMyD88. Additionally, the results showed that the expression levels of TLR1, TLR2 and TLR3 were different in response to Vibrio anguillarum, Lactobacillus plantarum and Aeromonas hydrophila infections. However, these bacteria significantly increased the expression levels of MyD88 and prophenoloxidase. These data suggest that the TLR-mediated signaling pathway is MyD88-dependent in response to pathogenic and probiotic bacteria in M. rosenbergii.

Molluscan Compounds Provide Drug Leads for the Treatment and Prevention of Respiratory Disease

Respiratory diseases place an immense burden on global health and there is a compelling need for the discovery of new compounds for therapeutic development. Here, we identify research priorities by critically reviewing pre-clinical and clinical studies using extracts and compounds derived from molluscs, as well as traditional molluscan medicines, used in the treatment of respiratory diseases. We reviewed 97 biomedical articles demonstrating the anti-inflammatory, antimicrobial, anticancer, and immunomodulatory properties of >320 molluscan extracts/compounds with direct relevance to respiratory disease, in addition to others with promising bioactivities yet to be tested in the respiratory context. Of pertinent interest are compounds demonstrating biofilm inhibition/disruption and antiviral activity, as well as synergism with approved antimicrobial and chemotherapeutic agents. At least 100 traditional medicines, incorporating over 300 different mollusc species, have been used to treat respiratory-related illness in cultures worldwide for thousands of years. These medicines provide useful clues for the discovery of bioactive components that likely underpin their continued use. There is particular incentive for investigations into anti-inflammatory compounds, given the extensive application of molluscan traditional medicines for symptoms of inflammation, and shells, which are the principal molluscan product used in these preparations. Overall, there is a need to target research toward specific respiratory disease-related hypotheses, purify bioactive compounds and elucidate their chemical structures, and develop an evidence base for the integration of quality-controlled traditional medicines.

A Siglec-1-like lectin from Nile tilapia (Oreochromis niloticus) possesses functions of agglutination and mediation of macrophage phagocytic activity

Siglec-1, one of the sialic acid-binding immunoglobulin-type lectins, is closely related to the recognition of host-pathogen and cell-cell interactions in the adaptive and innate immune systems. In this communication, a Siglec-1-like gene (OnSiglec-1-like) from Nile tilapia (Oreochromis niloticus) was analyzed. Relative expression revealed that the OnSiglec-1-like was expressed in all tested tissues, and the highest expression was found in the anterior kidney. Upon Streptococcus agalactiae (S. agalactiae) infection, the expression of OnSiglec-1-like was up-regulated in anterior kidney and spleen significantly in vivo. Additionally, the same phenomenon was observed in anterior kidney leukocytes upon LPS and S. agalactiae challenges as well in vitro. Western-blotting and ELISA analyses revealed that recombinant OnSiglec-1-like protein possessed high binding activity to LTA, LPS and S. agalactiae. Further, the recombinant OnSiglec-1-like was able to agglutinate S. agalactiae. Moreover, with the digestion of specific sialidase, the phagocytic ability of macrophages to S. agalactiae was greatly enhanced. Taken together, these results indicated that the Siglec-1-like possesses conserved functions of agglutination and promotion of macrophage phagocytic activity in Nile tilapia.

Identification and characterization of a novel galectin from the mud crab Scylla paramamosain

Galectins are a family of β-galactoside-binding lectins that play key roles in the invertebrate innate immunity system, but no galectin genes have been identified in the mud crab (Scylla paramamosain) so far. The present study is the first to clone a galectin gene (SpGal) from S. paramamosain, by the rapid amplification of cDNA ends technique based on expressed sequence tags. The full-length cDNA of SpGal was 3142 bp. Its open reading frame encoded a polypeptide of 280 amino acids containing a GLECT/Gal-bind lectin domain and a potential N-glycosylation site. The deduced amino acid sequence and multi-domain organization of SpGal were highly similar to those of invertebrate galectins, and phylogenetic analysis showed that SpGal was closely related to galectin isolated from Portunus trituberculatus. The mRNA transcripts of SpGal were found to be constitutively expressed in a wide range of tissues, with its expression level being higher in the hepatopancreas, gill, and hemocytes. The mRNA expression level of SpGal increased rapidly after the crabs were stimulated by Vibrio alginolyticus, and the maximum expression appeared at 6 h after the challenge. The lipopolysaccharide-binding ability of SpGal was dependent on its concentration, and it also exhibited agglutination activity with three Gram-negative (Aeromonas hydrophila, Chryseobacterium indologenes and Vibrio alginolyticus) and three Gram-positive (Bacillus aquimaris, Staphylococcus aureus and Micrococcus lysodeik) bacterial strains. In addition, hemagglutination activity with rabbit erythrocytes was observed in the absence of d-galactose. These results indicate that SpGal in S. paramamosain acts as a pattern recognition receptor to recognize a broad spectrum of microbes. The findings together indicate that SpGal plays an important role in the innate immune mechanisms of S. paramamosain against pathogenic infection.

Sialic acid and biology of life: An introduction

Sialic acids are important molecule with high structural diversity. They are known to occur in higher animals such as Echinoderms, Hemichordata, Cephalochorda, and Vertebrata and also in other animals such as Platyhelminthes, Cephalopoda, and Crustaceae. Plants are known to lack sialic acid. But they are reported to occur in viruses, bacteria, protozoa, and fungi. Deaminated neuraminic acid although occurs in vertebrates and bacteria, is reported to occur in abundance in the lower vertebrates. Sialic acids are mostly located in terminal ends of glycoproteins and glycolipids, capsular and tissue polysialic acids, bacterial lipooligosaccharides/polysaccharides, and in different forms that dictate their role in biology. Sialic acid play important roles in human physiology of cell-cell interaction, communication, cell-cell signaling, carbohydrate-protein interactions, cellular aggregation, development processes, immune reactions, reproduction, and in neurobiology and human diseases in enabling the infection process by bacteria and virus, tumor growth and metastasis, microbiome biology, and pathology. It enables molecular mimicry in pathogens that allows them to escape host immune responses. Recently sialic acid has found role in therapeutics. In this chapter we have highlighted the (i) diversity of sialic acid, (ii) their occurrence in the diverse life forms, (iii) sialylation and disease, and (iv) sialic acid and therapeutics.

A sialic acid-binding lectin with bactericidal and opsonic activities from Ruditapes philippinarum

In the present study, a sialic acid-binding lectin was cloned and characterized from Manila clam Ruditapes philippinarum (designed as RpSabl). The open reading frame of RpSabl encoded a polypeptide of 162 amino acids with a calculated molecular mass of 17.7 kDa. Analysis of the conserved domain suggested that RpSabl was a new member of the sialic acid-binding lectins family. In non-stimulated clams, RpSabl transcripts were constitutively expressed in all five tested tissues, especially in hepatopancreas. After Vibrio anguillarum challenge, the expression of RpSabl mRNA in hepatopancreas was significantly up-regulated at 3 h (3.8-fold, P < 0.05), 6 h (4.9-fold, P < 0.05), 12 h (12.3-fold, P < 0.01) and 24 h (9.7-fold, P < 0.01), while RpSabl transcripts in hemocytes was only significantly up-regulated at 6 h (8.5-Fold, P < 0.01). RNAi-mediated knockdown of RpSabl transcripts affected the survival rates of Manila clam against V. anguillarum, perhaps mainly due to the inhibited expression of antibacterial effectors (e.g. lysozyme and defensin). Moreover, recombinant protein of RpSabl (rRpSabl) possessed binding activities towards lipopolysaccharides (LPS), peptidoglycan (PGN) and glucan in vitro. Coinciding with the Pathogen-associated molecular patterns (PAMPs) binding assay, rRpSabl displayed broad bacterial-agglutination properties towards Vibrio harveyi, Vibrio splendidus, V. anguillarum, Enterobacter cloacae and Aeromonas hydrophila. Meanwhile, the phagocytosis and encapsulation ability of hemocytes could be significantly enhanced by rRpSabl incubation. All these results showed that RpSabl could function as a versatile molecule involved in the innate immune responses of R. philippinarum.

Immune recognition, antimicrobial and opsonic activities mediated by a sialic acid binding lectin from Ruditapes philippinarum

In the present study, a sialic acid-binding lectin was identified and characterized from Manila clam Ruditapes philippinarum (designed as RpSABL-1). Multiple alignments strongly suggested that RpSABL-1 was a new member of the sialic acid-binding lectin family. In non-stimulated clams, RpSABL-1 transcripts were constitutively expressed in all five tested tissues, especially in hepatopancreas. After Vibrio anguillarum challenge, the expression of RpSABL-1 mRNA was significantly up-regulated at 6 h (P < 0.05), 12 h (P < 0.01) and 24 h (P < 0.01). Recombinant RpSABL-1 protein (rRpSABL-1) displayed apparent binding activities towards lipopolysaccharides (LPS) and peptidoglycan (PGN), but not to glucan or chitin in vitro. Coinciding with the PAMPs binding assay, rRpSABL-1 exhibited obvious agglutination activities against Gram-positive bacterium Staphyloccocus aureus, Gram-negative bacteria Escherichia coli, V. anguillarum and Vibrio harveyi. Meanwhile, rRpSABL-1 showed antibacterial activities against E. coli, and biofilm formation of E. coli could also be inhibited after incubated with rRpSABL-1. Moreover, the encapsulation, phagocytosis and chemotactic ability of hemocytes could be enhanced by rRpSABL-1. All these results suggested that RpSABL-1 could function as a pattern recognition receptor with versatile functions in the innate immune responses of R. philippinarum.

Tissue distribution and functional characterization of mytimacin-4 in Mytilus galloprovincialis

Antimicrobial peptides (AMPs) play fundamental roles in the innate immunity of invertebrates. Mytimacin-4 is a kind of AMP gene previously sequenced from Mytilus galloprovincialis based on an identified EST sequence in our lab. In the present study, the tissue distribution and antimicrobial activities of mytimacin-4 were further investigated. A qRT-PCR analysis revealed that mytimacin-4 transcripts were constitutively expressed in all of the tested tissues of M. galloprovincialis, with the highest expression level in the posterior adductor muscle. After challenge by Vibrio anguillarum, the expression level of mytimacin-4 gene was significantly increased at 24 h (P < 0.05) in the mantle and increased at 48 h (P < 0.05) in the posterior adductor muscle. This finding suggested that mytimacin-4 transcripts were inducible upon pathogen infection. A minimal inhibitory concentration (MIC) assay indicated that recombinant mytimacin-4 protein had potent antimicrobial activities against gram-positive and gram-negative bacteria. Among the tested microorganisms, mytimacin-4 protein exhibited strong inhibition activities against Bacillus subtilis and Vibrio parahaemolyticus with MICs of 0.315 μM and 0.62 μM, respectively. This study provides for the first time direct evidence of antimicrobial action of mytimacin-4 in M. galloprovincialis.

A peptidoglycan recognition protein involved in immune recognition and immune defenses in Ruditapes philippinarum

Peptidoglycan recognition proteins (PGRPs) are important pattern recognition receptors in the innate immune system of invertebrates. In the study, a short PGRP (designed as RpPGRP) was identified and characterized from the manila clam Ruditapes philippinarum. The open reading frame of RpPGRP encoded a polypeptide of 249-amino acids with a calculated molecular mass of 27.2 kDa and an isoelectric point of 6.62. Multiple alignments and phylogenetic analysis strongly suggested that RpPGRP was a new member of the PGRP superfamily. In non-stimulated clams, RpPGRP exhibited different tissue expression pattern, and highly expressed in hepatopancreas and hemocytes. Expression of RpPGRP transcripts was significantly up-regulated in hemocytes of clams post Vibrio anguillarum or Micrococcus luteus challenge. The recombinant RpPGRP (rRpPGRP) exhibited high affinity to PGN, LPS and zymosan in a concentration-dependent manner. With a broad spectrum of bacterial binding activities, rRpPGRP exhibited strong agglutination activity to Escherichia coli, Vibrio splendidus, V. anguillarum and M. luteus. Furthermore, rRpPGRP exhibited Zn²⁺-dependent amidase activity and catalyzed the degradation of insoluble PGN. Especially, rRpPGRP exhibited significant antibacterial activity against E. coli and M. luteus. Moreover, the biofilm formation of E. coli could be inhibited after rRpPGRP incubation in the presence of Zn²⁺. This inhibitory effect of rRpPGRP might attribute to its amide bactericidal activity. Taken together, rRpPGRP played important roles in PGRP-mediated immune defense mechanisms, especially by recognizing antigens and eliminating bacteria.

Galactoside-binding lectin in Solen grandis as a pattern recognition receptor mediating opsonization

Galactoside-binding lectin (galectin) is a type of pathogen recognition molecule that occupies an important position in the invertebrate innate immunity system. Our previous study has identified a galectin gene in mollusk Solen grandis (SgGal-1) and illustrated its potential roles in innate immunity. By the functional study using recombinant protein and specific antibody, here, we confirmed the pivotal roles of SgGal-1 in immune defense of S. grandis. SgGal-1 protein was expressed in many tested tissues including gill, mantle, hepatopancreas and gonad, except hemocytes and muscle. The recombinant SgGal-1 (rSgGal-1) bound PGN and β-glucan instead of LPS in vitro, and it further caused significant agglutination of five different microbes, suggesting SgGal-1 served as a pattern recognition receptor (PRR) involved in immune defense of mollusk. Furthermore, SgGal-1 recruited hemocytes to encapsulate, which was blocked by anti-rSgGal-1 serum. In the meantime, rSgGal-1 as well as promoted the phagocytosis of hemocytes against Escherichia coli in vitro. All these results suggested that SgGal-1 in S. grandis not only acted as a PRR recognizing microbes but also directly participated in the process of immune opsonization to protect the host from pathogenic infection.