Calreticulin functions in antimicrobial immunity of obscure puffer Takifugu obscurus

Establishment and characterization of a fin cell line from Takifugu obscurus and its application to fish immunology

Takifugu obscurus (pufferfish) is an important species in aquaculture and has become widely popular in China and Japan. However, the development of the pufferfish aquaculture industry has been significantly impacted by severe diseases. Fish cell lines, as a model for in vitro studies, have the advantages of low cost, easy culture, and low genetic variation rate. A novel cell line from the fin of T. obscurus was established in this study and named TOF. TOF grew optimally with L-15 medium at 28°C and showed a multipolar fibroblast-like morphology. Mitochondrial cytochrome oxidase subunit 1 (COI) gene identification and karyotype detection confirmed that TOF cells originated from T. obscurus and the chromosome number was 44 (2n = 44). Transfection experiments showed that TOF cells were able to transfect and express exogenous genes by lipofection and electroporation. The studies of salinity (NaCl) and alkalinity (NaHCO3) on TOF proliferation showed that the highest multiplication rate of TOF was obtained at 6‰ NaCl mass and 4 g/L alkalinity, respectively. Furthermore, the expressions of several genes associated with the immune response were significantly upregulated after stimulating TOF cells with lipopolysaccharide (LPS) and poly (I:C), including irf7, il10, myd88, and nod1. Additionally, the Aeromonas hydrophila infection assay with TOF cells showed that TOF cells were sensitive to bacteria, and pufferfish could promote antimicrobial activity through NLR/NF-κB pathway to regulate the production of cytokines. This study suggested that TOF cell line could be an advantageous in vitro model for the investigation of fish immunology and virology, and could assist us to better comprehend the T. obscurus immune response to bacterial invasion.

Pufferfish gasdermin Ea is a significant player in the defense against bacterial pathogens

Gasdermins (GSDMs) are proteins cleaved by caspase (CASP) to trigger pyroptosis. In teleosts, pyroptosis is mediated by gasdermin E (GSDME). The Pufferfish, Takifugu rubripes, possesses two GSDME orthologs: named TrGSDMEa and TrGSDMEb. TrGSDMEa is cleaved by CASP3/7 to liberate the N-terminal (NT) domain that can trigger pyroptosis in mammalian cells. However, the biological function of TrGSDMEa in pufferfish is unknown, and TrGSDMEb is poorly studied. We found that TrGSDMEb was cleaved by CASP1/3/6/7/8, but the resulting NT domain, despite its similarity to TrGSDMEa-NT domain in sequence and structure, failed to induce pyroptosis. TrGSDMEa and TrGSDMEb exhibited similar expression patterns in pufferfish under normal physiological conditions but were up- and downregulated, respectively, in expression during Vibrio harveyi and Edwardsiella tarda infection. Bacterial infection induced the activation of TrGSDMEa and CASP3/7 in pufferfish cells, resulting in pyroptosis accompanied with IL-1β production and maturation. Inhibition of TrGSDMEa-mediated pyroptosis via TrCASP3/7 reduced the death of pufferfish cells and augmented bacterial dissemination in fish tissues. Structure-oriented mutagenesis identified 16 conserved residues in teleost GSDMEa that were required for the pore formation or auto-inhibition of GSDMEa. This study illustrates the role of GSDMEa-mediated pyroptosis in teleost defense against bacterial pathogens and provides new insights into the structure-based function of vertebrate GSDME.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-024-00237-x.

Two novel teleost calreticulins PoCrt-1/2, with bacterial binding and agglutination activity, are involved in antibacterial immunity

Calreticulin (Crt), a conserved lectin-like pleiotropic protein, plays crucial roles in mammalian immune response. In fish, the immunological function of Crt is limited investigated. Herein, we studied the antibacterial immunity of two type of Crt homologues (i.e. PoCrt-1 and PoCrt-2) in Japanese flounder (Paralichthys olivaceus). PoCrt-1 and PoCrt-2 are composed of 419 and 427 amino acid residues respectively, with 69.09% overall sequence identities with each other. Both PoCrt-1 and PoCrt-2 contain a signal peptide and three functional domains i.e. N-, P- and C-domains. Both PoCrt-1 and PoCrt-2 were constitutively expressed at various tissues with highest expression level in liver, and obviously regulated by Edwardsiella tarda and Vibrio harveyi. Furthermore, recombinant PoCrt-1 and PoCrt-2 (rPoCrt-1 and rPoCrt-2) could bind to different Gram-negative bacteria with highest binding index with E. tarda. At same time, in vitro rPoCrt-1 and rPoCrt-2 could agglutinate E. tarda, V. harveyi, and Vibrio anguillarum, and inhibit the bacterial growth. Similarly, in vivo rPoCrt-1 and rPoCrt-2 could significantly suppress the dissemination of E. tarda. Overall, these observations add new insights into the antibacterial immunity of Crt in P. olivaceus.

Isolation, Identification, and Investigation of Pathogenic Bacteria From Common Carp (Cyprinus carpio) Naturally Infected With Plesiomonas shigelloides

Various bacterial diseases have caused great economic losses to the high-density and intensive aquaculture industry; however, the pathogenic mechanism underlying the large-scale challenged to caused by many bacteria remain unclear, making the prevention and treatment of these diseases difficult. In the present study, we isolated a bacterial strain from Cyprinus carpio having a typical bacterial disease and named it Cc2021. Through subsequent morphological observations, a regression challenge, biochemical identification, and 16S rRNA gene sequence analysis, we determined Cc2021 to be Plesiomonas shigelloides. Subsequently, we comprehensively investigated the pathogenicity of P. shigelloides in C. carpio through a regression challenge and assessed the underlying the pathogenic mechanism. Mortality results revealed that P. shigelloides is highly pathogenic and infects various tissues throughout the body, resulting in edema of the liver, spleen, and body and head kidneys. Histopathological analysis revealed obvious inflammation, bleeding, and necrosis in the intestine, spleen, and head kidney. The body’s immune tissues actively produce complement C3, superoxide dismutase, and lysozyme after a challenge to resist bacterial invasion. With regard to the underlying pathogenesis of P. shigelloides, comparative transcriptome analysis revealed 876 upregulated genes and 828 downregulated genes in the intestine of C. carpio after the challenge. Analysis of differentially expressed unigenes revealed the involvement of major immune pathways, particularly the TNF signaling pathway, interleukin (IL)-17 signaling pathway, and Toll-like receptor signaling pathway. The present study provides new valuable information on the immune system and defense mechanisms of P. shigelloides.

An Update of Lectins from Marine Organisms: Characterization, Extraction Methodology, and Potential Biofunctional Applications

Lectins are a unique group of nonimmune carbohydrate-binding proteins or glycoproteins that exhibit specific and reversible carbohydrate-binding activity in a non-catalytic manner. Lectins have diverse sources and are classified according to their origins, such as plant lectins, animal lectins, and fish lectins. Marine organisms including fish, crustaceans, and mollusks produce a myriad of lectins, including rhamnose binding lectins (RBL), fucose-binding lectins (FTL), mannose-binding lectin, galectins, galactose binding lectins, and C-type lectins. The widely used method of extracting lectins from marine samples is a simple two-step process employing a polar salt solution and purification by column chromatography. Lectins exert several immunomodulatory functions, including pathogen recognition, inflammatory reactions, participating in various hemocyte functions (e.g., agglutination), phagocytic reactions, among others. Lectins can also control cell proliferation, protein folding, RNA splicing, and trafficking of molecules. Due to their reported biological and pharmaceutical activities, lectins have attracted the attention of scientists and industries (i.e., food, biomedical, and pharmaceutical industries). Therefore, this review aims to update current information on lectins from marine organisms, their characterization, extraction, and biofunctionalities.