Shandong University JBC: a C-type lectin can inhibit shrimp hemolymph bacteria

Wang Jinxing, a second-rank special professor of Shandong University and Professor Gerardo R. Vasta of the University of Maryland, reported a C-type lectin in a new study published in the Journal of Biological Chemistry on March 11, 2014. It is MjHeCL), which can inhibit the microbial community in the hemolymph of P. monodon by regulating the expression of antibacterial peptides.
Healthy vertebrates or invertebrates form symbiota with different bacterial communities in the microenvironment they provide. In recent years, significant progress has been made in the study of this symbiotic establishment mechanism. In vertebrates, microorganisms mainly live on the outer surface of the animal such as the skin, or the cavity that directly contacts the external environment such as the intestine.
However, in some healthy invertebrates (such as shrimp), bacteria are not only found in the digestive tract, but also in the circulating hemolymph (Hemolymph). Currently, this phenomenon is also observed in other aquatic invertebrate species. In shrimp, the bacterial community in hemolymph is relatively low compared to intestinal flora, and usually includes some that can become opportunistic pathogens under stress conditions (such as those that may occur in an aquaculture environment) Strains.
However, the regulation mechanism of the homeostasis of the hemolymph flora is still largely unknown, and researchers have been unable to find factors that inhibit bacterial proliferation in this eutrophic environment. Although antimicrobial peptides (AMPs) that have been identified in shrimp hemolymph may be candidates for inhibitors, how bacteria are detected, how AMPs expression is regulated, and how they inhibit the proliferation of microorganisms in shrimp hemolymph , Still unknown.
Invertebrates lack vertebrate-specific antibody- and T / B cell adaptive immunity, and can only rely on physical barriers and innate immunity as protective agents for infectious diseases. Among the different recognition and effector innate immune factors, lectins and antimicrobial peptides play a key role in detecting, controlling or eliminating any potential pathogens, not only in invertebrates, but also in most vertebrates. By binding sugar chains on the surface of microorganisms (including lipopolysaccharides and peptidoglycans), invertebrate C-type lectins (CTLs) effectively participate in the initial stage of pathogen recognition not only through carbohydrate recognition domain (CRD), It is also involved in different antibacterial effector functions, such as fixation, phagocytosis and clearance, encapsulation, nodule formation, activation of the prophenoloxidase system / melanization, etc.
Therefore, invertebrate CTLs may bear more burden than vertebrate CTLs for pathogen identification and activation of pathways that cause antibacterial effector functions. In addition, according to the researchers, there is a larger subset of CTL proteins than mammals, insects and crustaceans. Through transcriptome analysis, it was found that the body fluid CTL of shrimp is composed of at least 49 members. Compared with other invertebrates and vertebrates, it is highly expanded and diverse.
In this study, the researchers identified and described a CTL highly expressed in blood cells, which is present in the plasma of the giant shrimp (Marsupenaeus japonicus) and has high commercial value. . japonicushemocyte C-type lectin). Although the expression of MjHeCL is not affected by the challenge of microbes, the researchers found that silencing its expression through RNA interference (RNAi) can cause the bacterial proliferation in the hemolymph of the shrimp to run out of control and eventually cause the shrimp to die. This phenomenon can be alleviated by injection of recombinant MjHeCL, which can restore knockout shrimp to a healthy state.
A mechanical analysis conducted by the researchers showed that MjHeCL can inhibit the proliferation of bacteria by regulating the expression of antimicrobial peptides. MjHeCL plays a key role in shrimp homeostasis, probably because it can recognize a wider range of hemolymph microbial components than other lectins. This study illustrates the role of MjHeCL in maintaining shrimp health and provides new insights into the biological significance of C-type lectins, the diverse and abundant lectin family in invertebrates.

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