Evolution of LPS recognition and signaling: The bony fish perspective

Gut microbiota dysbiosis triggered by salinity stress enhances systemic inflammation in spotted scat (Scatophagus argus)

As an ecological disturbance, salinity changes substantially impact aquatic organism health. Gut microbiota plays a pivotal role in host health and exhibits heightened sensitivity to environmental salinity stress; however, the potential correlative mechanisms between gut microbiota dysbiosis triggered by salinity changes and host health remain unclear. The present study conducted a 4-week stress experiment to investigate the precise impact of gut microbiota on the inflammatory response in Scatophagus argus under different salinities (0 ‰ [hyposaline group, HO], 25 ‰ [control group, CT], and 40 ‰ [hypersaline group, HE]). Our results revealed that both HO and HE stress significantly changed the relative abundances of Gram-negative bacteria and the impairment of intestinal barrier function. Subsequently, the levels of lipopolysaccharide (LPS) in the serum exhibited a significant increase, and the expression levels of genes (tlrs, myd88, irak1, irak4, and traf6) involving TLRs/MyD88/NF-κB signaling pathway and pro-inflammatory cytokines (il-6, il-8, il-1β, and tnf-α) in the representative immune organs were significantly upregulated. Conversely, the abundance of the anti-inflammatory gene (tgf-β1) and its protein contents in serum were decreased. Transplantation of the gut microbiota from S. argus exposed to varying salinities into germ-free Oryzias latipes resulted in an enhanced inflammatory response. Our results suggested that both HO and HE stress increased the presence of Gram-negative bacteria and disrupted the intestinal barrier, leading to elevated serum LPS and subsequent systemic inflammation in fish. These findings provide innovative insights into the influence of salinity manipulation strategies on the health of aquatic organisms, contributing to the mariculture management in coastal areas.

The role of SYK phosphorylation in LPS-induced immunoglobulin responses of B cells in large yellow croaker (Larimichthys crocea)

Spleen tyrosine kinase (SYK), a non-receptor protein tyrosine kinase, is a key component of B cell receptor signaling and can regulate multiple physiological functions of B cells in mammals. In this study, a SYK gene was cloned and characterized from large yellow croaker (Larimichthys crocea) (LcSYK), whose open reading frame consists of 1851 base pairs and encodes 616 amino acid residues. The predicted LcSYK protein contains two N-terminal tandem Src homology 2 domains and a C-terminal tyrosine kinase catalytic domain, and shares a high amino acid sequence identity with SYK sequences in other vertebrate species. LcSYK was mainly expressed in immune tissues, such as head kidney, trunk kidney, spleen, and gill. The mRNA expression of LcSYK in primary head kidney leukocytes was not changed at 12, 24, and 48 h after lipopolysaccharide (LPS) stimulation. LPS stimulation upregulated the mRNA expression and protein production of IgM in IgM+ B cells, accompanied by an increase in the phosphorylation level, but not the total protein level, of LcSYK. Moreover, when we used PRT062607 HCl to inhibit the phosphorylation of LcSYK, both mRNA expression and protein production of IgM in IgM+ B cells were significantly suppressed. These results suggest that SYK phosphorylation may play a role in LPS-induced IgM production by IgM+ B cells, improving our understanding of the role of SYK in immunoglobulin responses of B cells in fish.

Molecular evolution and functional characterization of PKC-α-like in Lamprey

Protein kinase C-α (PKC-α) is a serine/threonine protein kinase categorized within the lipid-regulated PKC family. Despite considerable research on PKC-α in various vertebrates, information about its presence and characteristics in lampreys-among the few extant jawed vertebrates and the most primitive-remains limited. In this study, we report the first identification of a PKC-α-like gene in lamprey by successfully cloning its coding region, composed of 1683 base pairs that encode 560 amino acids, from the constructed cDNA library of Lampetrajaponica. Sequence analysis demonstrated a high degree of homology between the PKC-α-like sequence in lamprey and those in other vertebrates. Phylogenetic analysis indicated that lamprey PKC-α-like occupies an intermediate position between vertebrates and invertebrates, supporting the principles of species evolution. Gene structure analysis revealed low conservation throughout evolution, possibly due to events like chromosomal rearrangements or homologous recombination which may have caused significant changes in gene arrangement patterns. Additionally, we generated polyclonal antibody against PKC-α-like and investigated its tissue distribution in Lampetrajaponica. Our results demonstrated widespread expression of PKC-α-like across all tissues with varying mRNA expression levels in response to different pathogenic stimuli. Specifically, PKC-α-like expression was consistently up-regulated in response to polyinosine-polycytidylic acid (Poly (I:C)) stimulation, especially in immune-related tissues. Furthermore, we confirmed that PKC-α-like is primarily localized in the cytoplasm of lamprey cells. Moreover, our findings indicate that PKC-α-like promotes cell proliferation, prompting us to undertake a preliminary investigation of the underlying molecular mechanisms. In summary, this study establishes a theoretical foundation for further exploration of the evolutionary process of PKC-α and its role in cell proliferation mechanisms.

Dietary L-glutamate modulates intestinal mucosal immunity of juvenile hybrid striped bass (Morone saxatilis ♀ × Morone chrysops ♂)

Introduction

L-Glutamate is a conditionally essential amino acid, meaning it can become essential under specific conditions, like stress or disease. It is an abundant intracellular amino acid crucial in immune responses. Supplementation of feed with key amino acids, such as glutamate, can optimize growth and have other health benefits for production animals. Most research on dietary amino acid supplementation has focused on mammalian models, thus this research turned to hybrid striped bass, a teleost fish of growing importance to the aquaculture industry. The study investigated the effects of dietary supplementation with 0% or 5% glutamate in hybrid striped bass on intestinal mucosal immunity.

Methods

The basal purified diet contained crystalline amino acids, including 3% L-glutamate. After an 8-week period of dietary supplementation with 5% glutamate followed by lipopolysaccharide stimulation, the intestinal mucosa was analyzed at the cellular and molecular levels to compare with the head kidney to assess potential changes in immune reactivity.

Results

One week after lipopolysaccharide stimulation, glutamate supplementation enhanced (P < 0.05) the whole-body growth of fish without lipopolysaccharide challenge, total respiratory burst (the sum of O2 - and H2O2 production) in head kidney leukocytes, the net production of H2O2 in intestinal mucosal leukocytes, and upregulation of expression of mRNAs for IL-1β, TNF-α, and IgT in the gut mucosa.

Discussion

Dietary supplementation with 5% L-glutamate may modulate intestinal mucosal immunity and improve growth in HSB to enhance disease resistance. Further research is needed to clarify the mechanism and cost-effective application.

Evaluation of organ developmental toxicity of environmental toxicants using zebrafish embryos

There is increasing global concern about environmental pollutants, such as heavy metals, plastics, pharmaceuticals, personal care products, and pesticides, which have been detected in a variety of environments and are likely to be exposed to nontarget organisms, including humans. Various animal models have been utilized for toxicity assessment, and zebrafish are particularly valuable for studying the toxicity of various compounds owing to their similarity to other aquatic organisms and 70% genetic similarity to humans. Their development is easy to observe, and transgenic models for organs such as the heart, liver, blood vessels, and nervous system enable efficient studies of organ-specific toxicity. This suggests that zebrafish are a valuable tool for evaluating toxicity in specific organs and forecasting the potential impacts on other nontarget species. This review describes organ toxicity caused by various toxic substances and their mechanisms in zebrafish.

Cortisol suppresses lipopolysaccharide-induced in vitro inflammatory response of large yellow croaker (Larimichthys crocea) via the glucocorticoid receptor and p38 mitogen-activated protein kinase pathways

Glucocorticoids (GCs) are well-established anti-inflammatory agents, with cortisol, an endogenous GC, exerting pivotal regulatory effects on normal physiological processes. However, the immune regulatory role of cortisol in teleost fish, particularly in inflammation induced by pathogenic infection, remains largely unexplored. Here, we revealed that lipopolysaccharide (LPS) triggers a pro-inflammatory response in the large yellow croaker (Larimichthys crocea), as evidenced by increased expression of key pro-inflammatory cytokines and activation of the mitogen-activated protein kinase (MAPK) signaling pathway. We further explored the immunosuppressive capacity of cortisol in LPS-stimulated large yellow croaker kidney cells (PCK cells) and in vitro tissues of the large yellow croaker. Our findings indicated that cortisol effectively suppresses LPS-induced overexpression of pro-inflammatory cytokines and p38 MAPK pathway activation. Moreover, the immunosuppressive effects of cortisol were reversed by pretreatment with mifepristone, a glucocorticoid receptor (GR) antagonist. Collectively, this study delineated the inhibitory role of cortisol in the LPS-induced inflammatory cascade in large yellow croaker and underscores the significance of GR in mediating this response. These insights advance our comprehension of GCs-mediated immune modulation and provide a theoretical basis for the application of cortisol in disease prevention and the selective breeding of disease-resistant traits in aquaculture.

TLR7 in channel catfish (Ictalurus punctatus) is expressed in the endolysosome and is stimulated by synthetic ssRNA analogs, imiquimod, and resiquimod

Toll-like receptors (TLRs) are pivotal pattern recognition receptors (PRRs) and key mediators of innate immunity. Despite the significance of channel catfish (Ictalurus punctatus) in comparative immunology and aquaculture, its 20 TLR genes remain largely functionally uncharacterized. In this study, our aim was to determine the catfish TLR7 agonists, signaling potential, and cellular localization. Using a mammalian reporter system, we identified imiquimod and resiquimod, typical ssRNA analogs, as potent catfish TLR7 agonists. Notably, unlike grass carp TLR7, catfish TLR7 lacks the ability to respond to poly (I:C). Confocal microscopy revealed predominant catfish TLR7 expression in lysosomes, co-localizing with the endosomal chaperone protein, UNC93B1. Furthermore, imiquimod stimulation elicited robust IFNb transcription in peripheral blood leukocytes isolated from adult catfish. These findings underscore the conservation of TLR7 signaling in catfish, reminiscent of mammalian TLR7 responses. Our study sheds light on the functional aspects of catfish TLR7 and contributes to a better understanding of its role in immune defense mechanisms.

Establishment and characterization of a golden pompano (Trachinotus blochii) fin cell line for applications in marine fish pathogen immunology

Pompano fishes have been widely farmed worldwide. As a representative commercial marine species of the Carangidae family, the golden pompano (Trachinotus blochii) has gained significant popularity in China and worldwide. However, because of rapid growth and high-density aquaculture, the golden pompano has become seriously threatened by various diseases. Cell lines are the most cost-effective resource for in vitro studies and are widely used for physiological and pathological research owing to their accessibility and convenience. In this study, we established a novel immortal cell line, GPF (Golden pompano fin cells). GPF has been passaged over 69 generations for 10 months. The morphology, adhesion and extension processes of GPF were evaluated using light and electron microscopy. GPF cells were passaged every 3 days with L-15 containing 20 % fetal bovine serum (FBS) at 1:3. The optimum conditions for GPF growth were 28 °C and a 20 % FBS concentration. DNA sequencing of 18S rRNA and mitochondrial 16S rRNA confirmed that GPF was derived from the golden pompano. Chromosomal analysis revealed that the number pattern of GPF was 48 chromosomes. Transfection experiments demonstrated that GPF could be utilized to express foreign genes. Furthermore, heavy metals (Cd, Cu, and Fe) exhibited dose-dependent cytotoxicity against GPF. After polyinosinic-polycytidylic acid (poly I:C) treatment, transcription of the retinoic acid-inducible gene I-like receptor (RLR) pathway genes, including mda5, mita, tbk1, irf3, and irf7 increased, inducing the expression of interferon (IFN) and anti-viral proteins in GPF cells. In addition, lipopolysaccharide (LPS) stimulation up-regulated the expression of inflammation-related factors, including myd88, irak1, nfκb, il1β, il6, and cxcl10 expression. To the best of our knowledge, this is the first study on the immune response signaling pathways of the golden pompano using an established fin cell line. In this study, we describe a preliminary investigation of the GPF cell line immune response to poly I:C and LPS, and provide a more rapid and efficient experimental material for research on marine fish immunology.

Trans-Cinnamaldehyde Primes More Robust Channel Catfish Immune Responses to Edwardsiella ictaluri Infection

Infection with Edwardsiella ictaluri, a causative agent of enteric septicemia of catfish, threatens profitable catfish production through inventory losses. We previously demonstrated that trans-cinnamaldehyde (TC) enhances the survival of catfish following E. ictaluri infection. The present study was conducted to investigate catfish immune responses to TC feeding and E. ictaluri infection. The expression of 13 proinflammatory, innate, and adaptive immune-related genes was evaluated over time in two sets of experiments using real-time polymerase chain reaction (PCR). In the first experiment, catfish were fed a basal diet with or without TC supplementation, while in the second they were fed a TC-supplemented or normal diet followed by infection with E. ictaluri. The catfish group infected with E. ictaluri and fed a TC-diet showed significant changes in the expression of innate and adaptive immune-related genes compared to control group. At 21 and 28 days post-infection, recovered fish showed significant increases in the expression of IgM in the anterior kidney and spleen. These results suggest that the supplemental dietary intake of TC can improve the immune status of catfish via engaging innate and adaptive immune responses and the production of memory cells in immunocompetent tissues. Together, this study provides an important foundation for the potential application of TC as an antimicrobial alternative in aquaculture.

The uses of zebrafish (Danio rerio) as an in vivo model for toxicological studies: A review based on bibliometrics

An in vivo model is necessary for toxicology. This review analyzed the uses of zebrafish (Danio rerio) in toxicology based on bibliometrics. Totally 56,816 publications about zebrafish from 2002 to 2023 were found in Web of Science Core Collection, with Toxicology as the top 6 among all disciplines. Accordingly, the bibliometric map reveals that "toxicity" has become a hot keyword. It further reveals that the most common exposure types include acute, chronic, and combined exposure. The toxicological effects include behavioral, intestinal, cardiovascular, hepatic, endocrine toxicity, neurotoxicity, immunotoxicity, genotoxicity, and reproductive and transgenerational toxicity. The mechanisms include oxidative stress, inflammation, autophagy, and dysbiosis of gut microbiota. The toxicants commonly evaluated by using zebrafish model include nanomaterials, arsenic, metals, bisphenol, and dioxin. Overall, zebrafish provide a unique and well-accepted model to investigate the toxicological effects and mechanisms. We also discussed the possible ways to address some of the limitations of zebrafish model, such as the combination of human organoids to avoid species differences.

The zebrafish as a potential model for vaccine and adjuvant development

INTRODUCTION

Zebrafishes represent a proven model for human diseases and systems biology, exhibiting physiological and genetic similarities and having innate and adaptive immune systems. However, they are underexplored for human vaccinology, vaccine development, and testing. Here we summarize gaps and challenges.

AREAS COVERED

Zebrafish models have four potential applications: 1) Vaccine safety: The past successes in using zebrafishes to test xenobiotics could extend to vaccine and adjuvant formulations for general safety or target organs due to the zebrafish embryos' optical transparency. 2) Innate immunity: The zebrafish offers refined ways to examine vaccine effects through signaling via Toll-like or NOD-like receptors in zebrafish myeloid cells. 3) Adaptive immunity: Zebrafishes produce IgM, IgD,and two IgZ immunoglobulins, but these are understudied, due to a lack of immunological reagents for challenge studies. 4) Systems vaccinology: Due to the availability of a well-referenced zebrafish genome, transcriptome, proteome, and epigenome, this model offers potential here.

EXPERT OPINION

It remains unproven whether zebrafishes can be employed for testing and developing human vaccines. We are still at the hypothesis-generating stage, although it is possible to begin outlining experiments for this purpose. Through transgenic manipulation, zebrafish models could offer new paths for shaping animal models and systems vaccinology.

Immunonutrition: facilitating mucosal immune response in teleost intestine with amino acids through oxidant-antioxidant balance

Comparative animal models generate fundamental scientific knowledge of immune responses. However, these studies typically are conducted in mammals because of their biochemical and physiological similarity to humans. Presently, there has been an interest in using teleost fish models to study intestinal immunology, particularly intestinal mucosa immune response. Instead of targeting the pathogen itself, a preferred approach for managing fish health is through nutrient supplementation, as it is noninvasive and less labor intensive than vaccine administrations while still modulating immune properties. Amino acids (AAs) regulate metabolic processes, oxidant-antioxidant balance, and physiological requirements to improve immune response. Thus, nutritionists can develop sustainable aquafeeds through AA supplementation to promote specific immune responses, including the intestinal mucosa immune system. We propose the use of dietary supplementation with functional AAs to improve immune response by discussing teleost fish immunology within the intestine and explore how oxidative burst is used as an immune defense mechanism. We evaluate immune components and immune responses in the intestine that use oxidant-antioxidant balance through potential selection of AAs and their metabolites to improve mucosal immune capacity and gut integrity. AAs are effective modulators of teleost gut immunity through oxidant-antioxidant balance. To incorporate nutrition as an immunoregulatory means in teleost, we must obtain more tools including genomic, proteomic, nutrition, immunology, and macrobiotic and metabonomic analyses, so that future studies can provide a more holistic understanding of the mucosal immune system in fish.

Immune Transcriptional Response in Head Kidney Primary Cell Cultures Isolated from the Three Most Important Species in Chilean Salmonids Aquaculture

Fish cell culture is a common in vitro tool for studies in different fields such as virology, toxicology, pathology and immunology of fish. Fish cell cultures are a promising help to study how to diagnose and control relevant viral and intracellular bacterial infections in aquaculture. They can also be used for developing vaccines and immunostimulants, especially with the ethical demand aiming to reduce and replace the number of fish used in research. This study aimed to isolate head kidney primary cell cultures from three Chilean salmonids: Salmo salar, Oncorhynchus kisutch, and Oncorhynchus mykiss, and characterize the response to bacterial and viral stimuli by evaluating various markers of the innate and adaptive immune response. Specifically, the primary cell cultures of the head kidney from the three salmonids studied were cultured and exposed to two substances that mimic molecular patterns of different pathogens, i.e., Lipopolysaccharide (LPS) (bacterial) and Polyinosinic: polycytidylic acid (POLY I:C). Subsequently, we determined the mRNA expression profiles of the TLR-1, TLR-8, IgM, TLR-5, and MHC II genes. Head kidney primary cell cultures from the three species grown in vitro responded differently to POLY I:C and LPS. This is the first study to demonstrate and characterize the expression of immune genes in head kidney primary cell culture isolated from three salmonid species. It also indicates their potential role in developing immune responses as defense response agents and targets of immunoregulatory factors.