Mindin Activates Autophagy for Lipid Utilization and Facilitates White Spot Syndrome Virus Infection in Shrimp.

Mindin is a secreted extracellular matrix protein that is involved in regulating cellular events through interacting with integrin. Studies have demonstrated its role in host immunity, including phagocytosis, cell migration, and cytokine production. However, the function of Mindin in the host-virus interaction is largely unknown. In the present study, we report that Mindin facilitates virus infection by activating lipid utilization in an arthropod, kuruma shrimp (Marsupenaeus japonicus). Shrimp Mindin facilitates white spot syndrome virus infection by facilitating viral entry and replication. By activating autophagy, Mindin induces lipid droplet consumption, the hydrolysis of triglycerides into free fatty acids, and ATP production, ultimately providing energy for virus infection. Moreover, integrin is essential for Mindin-mediated autophagy and lipid utilization. Therefore, by revealing the mechanism by which Mindin facilitates virus infection through regulating lipid metabolism, the present study reveals the significance of Mindin in the host-virus interaction. IMPORTANCE White spot syndrome virus (WSSV) is an enveloped double-stranded DNA virus that has had a serious influence on worldwide shrimp farming in the last 30 years. We have demonstrated that WSSV hijacks host autophagy and lipid metabolism for reproduction in kuruma shrimp (Marsupenaeus japonicus). These findings revealed the mechanism by which WSSV exploits host machinery for its infection and provided serial targets for WSSV prevention and control in shrimp farming.

Complement-related proteins in crustacean immunity.

As an important part of innate immune system, complement system is widely involved in defense response and immune regulation, and plays an important biological role. The complement system has been deeply studied. More than 30 complement-related molecules and three major complement-activation pathways have been identified in vertebrates. Crustacean animals do not have complement system. There are only some complement-related proteins in crustaceans which are important for host defense. In this review, we summarize the current knowledge about complement-related proteins in crustaceans, and their functions in crustacean immunity. We also make a comparation of the crustacean pro-phenoloxidase activating system and the mammalian complement system. This review provides a better understanding of the evolution and function of complement-related proteins in crustaceans.

Shoc2 recognizes bacterial flagellin and mediates antibacterial Erk/Stat signaling in an invertebrate.

Flagellin is a key bacterial virulence factor that can stimulate molecular immune signaling in both animals and plants. The detailed mechanisms of recognizing flagellin and mounting an efficient immune response have been uncovered in vertebrates; however, whether invertebrates can discriminate flagellin remains largely unknown. In the present study, the homolog of human SHOC2 leucine rich repeat scaffold protein in kuruma shrimp (Marsupenaeus japonicus), designated MjShoc2, was found to interact with Vibrio anguillarum flagellin A (FlaA) using yeast two-hybrid and pull-down assays. MjShoc2 plays a role in antibacterial response by mediating the FlaA-induced expression of certain antibacterial effectors, including lectin and antimicrobial peptide. FlaA challenge, via MjShoc2, led to phosphorylation of extracellular regulated kinase (Erk), and the subsequent activation of signal transducer and activator of transcription (Stat), ultimately inducing the expression of effectors. Therefore, by establishing the FlaA/MjShoc2/Erk/Stat signaling axis, this study revealed a new antibacterial strategy in shrimp, and provides insights into the flagellin sensing mechanism in invertebrates.

Interferon functional analog activates antiviral Jak/Stat signaling through integrin in an arthropod.

Drosophila Vago is a small antiviral peptide. Its ortholog in Culex mosquito was found to be an interferon-like cytokine that limits virus replication through activating Jak/Stat signaling. However, this activation is independent of Domeless, the sole homolog of vertebrate type I cytokine receptor. How Vago activates the Jak/Stat pathway remains unknown. Herein, we report this process is dependent on integrin in kuruma shrimp (Marsupenaeus japonicus). Shrimp Vago-like (MjVago-L) plays an antiviral role by activating the Jak/Stat pathway and inducing Stat-regulated Ficolin. Blocking integrin abrogates the role of MjVago-L. The interaction between MjVago-L and integrin ß3 is confirmed. An Asp residue in MjVago-L is found critical for the interaction and MjVago-L's antiviral role. Moreover, Fak, a key adaptor of integrin signaling, mediates MjVago-L-induced Jak/Stat activation. Therefore, this study reveals that integrin, as the receptor of MjVago-L, mediates Jak/Stat activation. The establishment of the MjVago-L/integrin/Fak/Jak/Stat/Ficolin axis provides insights into antiviral cytokine signaling in invertebrates.

Maturation of an Antimicrobial Peptide Inhibits Aeromonas hydrophila Infection in Crayfish.

Rapid synthesis and release of active antimicrobial peptides (AMPs) is an important strategy in innate immune. Processing of the precursor into the active form is a common posttranslational modification of AMPs in mammals. However, in invertebrates, the mechanism of AMP maturation is largely unknown. In the current study, to our knowledge, a novel potential AMP, designated as PcnAMP, was identified because of its significant induction by bacterial infection in the red swamp crayfish (Procambarus clarkii). PcnAMP was cleaved into a short fragment postinfection. Using the purified native peptide, this cleavage was found to be mediated by trypsin after synthesis. Proteolysis produced an N-terminal peptide that exerted the antibacterial function. Although the N-terminal peptide did not show significant similarity to any other sequences, it was predicted to have an overall helical structure and high amphipathicity, both of which are typical features of many AMPs. The N-terminal active peptide exhibited a wide spectrum of antimicrobial activity. Atomic force microscope imaging and flow cytometry analysis showed that treatment with the active form of PcnAMP led to the collapse of the bacterial cell wall and permeabilization of the bacterial cell membrane. Thus, this study provided a new candidate for therapeutic agent development, and revealed new insights into the maturation of AMPs in invertebrates.