Goldfish (Carassius auratus L.) as a model system to study the growth factors, receptors and transcription factors that govern myelopoiesis in fish

The Modulation of Septic Shock: A Proteomic Approach

Sepsis poses a significant challenge due its lethality, involving multiple organ dysfunction and impaired immune responses. Among several factors affecting sepsis, monocytes play a crucial role; however, their phenotype, proteomic profile, and function in septic shock remain unclear. Our aim was to fully characterize the subpopulations and proteomic profiles of monocytes seen in septic shock cases and discuss their possible impact on the disease. Peripheral blood monocyte subpopulations were phenotype based on CD14/CD16 expression by flow cytometry, and proteins were extracted from the monocytes of individuals with septic shock and healthy controls to identify changes in the global protein expression in these cells. Analysis using 2D-nanoUPLC-UDMSE identified 67 differentially expressed proteins in shock patients compared to controls, in which 44 were upregulated and 23 downregulated. These proteins are involved in monocyte reprogramming, immune dysfunction, severe hypotension, hypo-responsiveness to vasoconstrictors, vasodilation, endothelial dysfunction, vascular injury, and blood clotting, elucidating the disease severity and therapeutic challenges of septic shock. This study identified critical biological targets in monocytes that could serve as potential biomarkers for the diagnosis, prognosis, and treatment of septic shock, providing new insights into the pathophysiology of the disease.

Biology and functions of fish thrombocytes: A review

This comprehensive review examines the role of fish thrombocytes, cells considered functionally analogous to platelets in terms of coagulation, but which differ in their origin and morphology. Despite the evolutionary distance between teleosts and mammals, genomic studies reveal conserved patterns in blood coagulation, although there are exceptions such as the absence of factors belonging to the contact system. Beyond coagulation, fish thrombocytes have important immunological functions. These cells express both proinflammatory genes and genes involved in antigen presentation, suggesting a role in both innate and adaptive immune responses. Moreover, having demonstrated their phagocytic abilities, crucial in the fight against pathogenic microorganisms, underscores their multifaceted involvement in immunity. Finally, the need for further research on the functions of these cells is highlighted, in order to better understand their involvement in maintaining the health of aquaculture fish. The use of standardized and automated methods for the analysis of these activities is advocated, emphaiszing their potential to facilitate the early detection of stress or infection, thus minimizing the economic losses that these adverse situations can generate in the field of aquaculture.

Profiling the Physiological Roles in Fish Primary Cell Culture

Fish primary cell culture has emerged as a valuable tool for investigating the physiological roles and responses of various cell types found in fish species. This review aims to provide an overview of the advancements and applications of fish primary cell culture techniques, focusing on the profiling of physiological roles exhibited by fish cells in vitro. Fish primary cell culture involves the isolation and cultivation of cells directly derived from fish tissues, maintaining their functional characteristics and enabling researchers to study their behavior and responses under controlled conditions. Over the years, significant progress has been made in optimizing the culture conditions, establishing standardized protocols, and improving the characterization techniques for fish primary cell cultures. The review highlights the diverse cell types that have been successfully cultured from different fish species, including gonad cells, pituitary cells, muscle cells, hepatocytes, kidney and immune cells, adipocyte cells and myeloid cells, brain cells, primary fin cells, gill cells, and other cells. Each cell type exhibits distinct physiological functions, contributing to vital processes such as metabolism, tissue regeneration, immune response, and toxin metabolism. Furthermore, this paper explores the pivotal role of fish primary cell culture in elucidating the mechanisms underlying various physiological processes. Researchers have utilized fish primary cell cultures to study the effects of environmental factors, toxins, pathogens, and pharmaceutical compounds on cellular functions, providing valuable insights into fish health, disease pathogenesis, and drug development. The paper also discusses the application of fish primary cell cultures in aquaculture research, particularly in investigating fish growth, nutrition, reproduction, and stress responses. By mimicking the in vivo conditions in vitro, primary cell culture has proven instrumental in identifying key factors influencing fish health and performance, thereby contributing to the development of sustainable aquaculture practices.

Molecular and functional characterization of two granulocyte colony stimulating factors in goldfish (Carassius auratus L.)

Granulocyte colony-stimulating factor (GCSF) is a member of the hematopoietic growth factor family that acts primarily on neutrophils and neutrophilic precursors to promote cell proliferation and differentiation. Although multiple GCSF genes have been found in teleosts, knowledge of their functions during fish hematopoietic development is still limited. Here, we report for the first time the molecular and functional characterization of two goldfish GCSFs (gfGCSF-a and gfGCSF-b). The open reading frame (ORF) of the gfGCSF-a and gfGCSF-b cDNA transcript consisted respectively of 624 bp and 678 bp with its ORF encoding 207 and 225 amino acids (aa), with a 17 aa signal peptide for each gene and a conserved domain of the IL-6 superfamily. Treatment of goldfish head kidney leukocytes (HKLs) with LPS increased gfGCSF-a and gfGCSF-b mRNA expression levels, also exposure of HKLs to either heat-killed or live A. hydrophila, induced transcriptional upregulation of gfGCSF-a and gfGCSF-b levels. Recombinant gfGCSF-a and gfGCSF-b protein (rgGCSF-a and rgGCSF-b) induced a dose-dependent production of TNFα and IL-1β from goldfish neutrophils. In vitro experiments showed rgGCSF-a and rgGCSF-b differentially promoted the proliferation and differentiation of leukocytes in goldfish. Furthermore, treatment of HKLs with rgGCSF-a showed significant upregulation of mRNA levels of the hematopoietic transcription factor GATA2, Runx1, MafB, and cMyb, while gfGCSF-b induces not only all four transcriptional factors mentioned above but also CEBPα. Our results indicate that goldfish GCSF-a and GCSF-b are important regulators of neutrophil proliferation and differentiation, which could stimulate different stages and lineages of hematopoiesis.

Expression analysis of Carassius auratus-leukocyte-immune-type receptors (CaLITRs) during goldfish kidney macrophage development and in activated kidney leukocyte cultures

Carassius auratus leukocyte immune-type receptors (CaLITRs) were recently discovered immunoregulatory receptors in goldfish that have diverse immunoglobulin-like (Ig-like) ectodomains and intracellular signaling motifs. Genomic analysis shows that CaLITR-types are also located as distinct gene clusters across multiple goldfish chromosomes. For example, CaLITR1 (unplaced) is a functionally ambiguous receptor having two Ig-like domains, a transmembrane domain (TM), and a short cytoplasmic tail (CYT) devoid of any recognizable signaling motifs. CaLITR2 (Chr47) is a putative inhibitory receptor containing four Ig-like domains, a TM, and a long CYT with an immunoreceptor tyrosine-based inhibition motif (ITIM) and immunoreceptor tyrosine-based switch motif (ITSM). A putative activating receptor-type, CaLITR3 (Chr3), has four Ig-like domains, a TM, and a short CYT containing a positively charged histidine residue and CaLITR4 (ChrLG28B) is a receptor with putative multifunctional signaling potential as well as five Ig-like domains, a TM, and a long tyrosine-motif containing CYT region. The variable genomic locations of the CaLITRs suggest that they are likely under the influence of different cis- and/or trans-regulatory elements. To better understand the transcriptional activities of select CaLITRs from variable genomic regions, we used an RT-qPCR-based approach to examine the expression of CaLITR1, CaLITR2, CaLITR3, and CaLITR4 during goldfish primary kidney macrophage (PKM) development and in mixed leukocyte reaction cultures (MLRs) of the goldfish. Our results showed that the select CaLITRs are differentially expressed during PKM development and in goldfish MLRs exposed to T-cell mitogens/immunosuppressive drugs, supporting that the transcription of these CaLITRs is likely regulated by distinct cis- and/or trans-regulatory elements.

Characterization of Pipefish Immune Cell Populations Through Single-Cell Transcriptomics

Teleost adaptive immune systems have evolved with more flexibility than previously assumed. A particularly enigmatic system to address immune system modifications in the evolutionary past is represented by the Syngnathids, the family of pipefishes, seahorses and seadragons. These small fishes with their unique male pregnancy have lost the spleen as an important immune organ as well as a functional major histocompatibility class II (MHC II) pathway. How these evolutionary changes have impacted immune cell population dynamics have up to this point remained unexplored. Here, we present the first immune cell repertoire characterization of a syngnathid fish (Syngnathus typhle) using single-cell transcriptomics. Gene expression profiles of individual cells extracted from blood and head-kidney clustered in twelve putative cell populations with eight belonging to those with immune function. Upregulated cell marker genes identified in humans and teleosts were used to define cell clusters. While the suggested loss of CD4+ T-cells accompanied the loss of the MHC II pathway was supported, the upregulation of specific subtype markers within the T-cell cluster indicates subpopulations of regulatory T-cells (il2rb) and cytotoxic T-cells (gzma). Utilizing single-cell RNA sequencing this report is the first to characterize immune cell populations in syngnathids and provides a valuable foundation for future cellular classification and experimental work within the lineage.

Immunological memory in teleost fish

Immunological memory can be regarded as the key aspect of adaptive immunity, i.e. a specific response to first contact with an antigen, which in mammals is determined by the properties of T, B and NK cells. Re-exposure to the same antigen results in a more rapid response of the activated specific cells, which have a unique property that is the immunological memory acquired upon first contact with the antigen. Such a state of immune activity is also to be understood as related to "altered behavior of the immune system" due to genetic alterations, presumably maintained independently of the antigen. It also indicates a possible alternative mechanism of maintaining the immune state at a low level of the immune response, "directed" by an antigen or dependent on an antigen, associated with repeated exposure to the same antigen from time to time, as well as the concept of innate immune memory, associated with epigenetic reprogramming of myeloid cells, i.e. macrophages and NK cells. Studies on Teleostei have provided evidence for the presence of immunological memory determined by T and B cells and a secondary response stronger than the primary response. Research has also demonstrated that in these animals macrophages and NK-like cells (similar to mammalian NK cells) are able to respond when re-exposed to the same antigen. Regardless of previous reports on immunological memory in teleost fish, many reactions and mechanisms related to this ability require further investigation. The very nature of immunological memory and the activity of cells involved in this process, in particular macrophages and NK-like cells, need to be explained. This paper presents problems associated with adaptive and innate immune memory in teleost fish and characteristics of cells associated with this ability.

Identification of goldfish (Carassius auratus L.) leukocyte immune-type receptors shows alternative splicing as a potential mechanism for receptor diversification

Leukocyte immune-type receptors (LITRs) are a multigene family of teleost immunoregulatory proteins that share structural, phylogenetic, and likely functional relationships with several innate immune receptor proteins in other vertebrates, including mammals. Originally discovered in channel catfish (Ictalurus punctatus), representative IpLITR-types have been shown to regulate diverse innate immune cell effector responses including phagocytosis, degranulation, and cytokine secretion. To date, IpLITRs have been primarily characterized using mammalian cell line expression systems, therefore many unanswered questions remain regarding their actual regulatory roles in fish immunity. In the present study, we report on the preliminary molecular characterization of five goldfish (Carassius auratus) CaLITR-types and the identification of several putative splice variants of these receptors cloned from various goldfish tissues and primary myeloid cell cultures. In general, CaLITR mRNA transcripts were detected in all goldfish tissues tested, and also in primary kidney macrophage and neutrophil cultures. Specifically, CaLITR1 is a functionally ambiguous receptor with no charged amino acids in its transmembrane (TM) segment and is devoid of tyrosine-based signaling motifs in its short cytoplasmic tail (CYT) region. CaLITR2 is a putative activating receptor-type that contains immunotyrosine-based activation motifs (ITAMs) within its long CYT region, and CaLITR3 has a positively charged TM segment, suggesting that it may recruit intracellular stimulatory adaptor signaling molecules. CaLITR4 and CaLITR5 appear to have diverse signaling capabilities since they contain various immunoregulatory signaling motifs within their CYT regions including putative Nck and STAT recruitment motifs as well as ITAM-like and ITIM sequences. We also identified putative CaLITR splice variants with altered extracellular Ig-like domain compositions and variable CYT regions. Interestingly, this suggests that alternative splicing-mediated diversification of CaLITRs can generate receptor forms with possible variable binding and/or intracellular signaling abilities. Overall, these findings reveal new information about the teleost LITRs and sets the stage for exploring how alternative splicing leads to the functional diversification of this complex multigene immunoregulatory receptor family.

A fish cytokine related to human IL-3, IL-5, and GM-CSF, induces development of eosinophil/basophil/mast-cell type (EBM) granulocytes

Interleukin-3 (IL-3), IL-5, and granulocyte-macrophage colony-stimulating factor (GM-CSF) are related cytokines that signal through receptors possessing the β common (βc) chain. As a family, these cytokines combine rather non-specific hematopoietic growth factor properties with a special importance for eosinophils, basophils, and mast cells. In fish the cytokines of this family are called IL-5fam, and the present study, using carp, constitutes their first functional analysis. Carp il-5fam expression was enhanced by stimulation with phytohemagglutinin and killed bacteria. Reminiscent of mammalian IL-3/IL-5/GM-CSF family members, recombinant carp IL-5fam (rcIL-5fam) induced activation of transcription factor STAT5 and efficiently promoted proliferation and colony-formation of eosinophil/basophil/mast-cell type (EBM) granulocytes. Upon addition of recombinant carp βc the growth effect of rcIL-5fam was reduced, suggesting βc participation in the signaling route. In summary, despite differences in individual cytokines and cell populations, fish and mammalian IL-3/IL-5/GM-CSF family members share growth factor functions for non-neutrophil granulocytes.

Characterization of miRNAs in Cultured Atlantic Salmon Head Kidney Monocyte-Like and Macrophage-Like Cells

Macrophages are among the first cells to respond to infection and disease. While microRNAs (miRNAs) are involved in the process of monocyte-to-macrophage differentiation in mammals, less is known in teleost fish. Here, Atlantic salmon head kidney leukocytes (HKLs) were used to study the expression of miRNAs in response to in vitro culture. The morphological analysis of cultures showed predominantly monocyte-like cells on Day 1 and macrophage-like cells on Day 5, suggesting that the HKLs had differentiated from monocytes to macrophages. Day 5 HKLs also contained a higher percentage of phagocytic cells. Small RNA sequencing and qPCR analysis were applied to examine the miRNA diversity and expression. There were 370 known mature Atlantic salmon miRNAs in HKLs. Twenty-two miRNAs (15 families) were downregulated while 44 miRNAs (25 families) were upregulated on Day 5 vs. Day 1. Mammalian orthologs of many of the differentially expressed (DE) miRNAs are known to regulate macrophage activation and differentiation, while the teleost-specific miR-2188, miR-462 and miR-731 were also DE and are associated with immune responses in fish. In silico predictions identified several putative target genes of qPCR-validated miRNAs associated with vertebrate macrophage differentiation. This study identified Atlantic salmon miRNAs likely to influence macrophage differentiation, providing important knowledge for future functional studies.

Characterisation of Thrombocytes in Osteichthyes

Thrombocytes in vertebrates other than mammals, inter alia in fish, are analogues of platelets in mammals. In Osteichthyes, these cells take part in haemostatic processes, including aggregation and release reactions in cases of blood vessel damage, and in the immune response development as well. This paper discusses the development of thrombocytes in Osteichthyes, taking into account the need to make changes to the concept of grouping progenitor cells as suggested in the literature. The following pages present the morphological and cytochemical properties of thrombocytes as well as their defence functions, and also point out differences between thrombocytes in fish and platelets in mammals. The paper further highlights the level of thrombocytes' immune activity observed in fish and based on an increased proportion of these cells in response to antigenic stimulation, on morphological shifts towards forms characteristic of dendritic cells after antigenic stimulation and on the presence of surface structures and cytokines released through, inter alia, gene expression of TLR receptors, MHC class II protein-coding genes and pro-inflammatory cytokines. The study also points out the need to recognise thrombocytes in Osteichthyes as specialised immune cells conditioning non-specific immune mechanisms and playing an important role in affecting adaptive immune mechanisms.

Paralogs of Common Carp Granulocyte Colony-Stimulating Factor (G-CSF) Have Different Functions Regarding Development, Trafficking and Activation of Neutrophils

Mammalian granulocyte colony-stimulating factor (G-CSF; CSF3) is a primary cytokine that promotes the development, mobilization, and activation of neutrophils and their precursors. Teleosts have been reported to possess two paralogs as a likely result of the teleost-wide whole genome duplication (WGD) event, but functional divergence of G-CSF paralogs remains poorly understood. Common carp are an allotetraploid species owing to an additional WGD event in the carp lineage and here, we report on genomic synteny, sequence similarity, and phylogeny of four common carp G-CSF paralogs (g-csfa1 and g-csfa2; g-csfb1 and g-csfb2). G-csfa1 and g-csfa2 show differential and relatively high gene expression levels, while g-csfb1 and g-csfb2 show low basal gene expression levels in most tissues. All paralogs are expressed higher in macrophages than in other leukocyte sub-types and are highly up-regulated by treatment of macrophages with mitogens. Recombinant G-CSFa1 and G-CSFb1 both promoted the proliferation of kidney hematopoietic cells, while only G-CSFb1 induced the differentiation of kidney cells along the neutrophil-lineage. Colony-forming unit assays revealed that G-CSFb1 alone stimulates the formation of CFU-G colonies from head- and trunk-kidney whereas the combination of G-CSFa1 and G-CSFb1 stimulates the formation of both CFU-G and CFU-GM colonies. Recombinant G-CSFa1 and G-CSFb1 also exhibit chemotactic activity against kidney neutrophils and up-regulation of cxcr1 mRNA expression was highest in neutrophils after G-CSFb1 stimulation. Furthermore, G-CSFb1 more than G-CSFa1 induced priming of kidney neutrophils through up-regulation of a NADPH-oxidase component p47 phox . In vivo administration of G-CSF paralogs increased the number of circulating blood neutrophils of carp. Our findings demonstrate that gene duplications in teleosts can lead to functional divergence between paralogs and shed light on the sub-functionalization of G-CSF paralogs in cyprinid fish.

Anaesthetics and analgesics used in adult fish for research: A review

The number of fish used in research has increased in the last decades. Anaesthesia is required when fish must be held immobile and it is crucial to promote fish welfare, because these vertebrates can show signs of stress and/or pain during handling, transport, tagging, sampling and invasive procedures. The use of an inadequate anaesthetic protocol can compromise not only the welfare of the fish, but also the reliability of the research results. Thus, the development of suitable anaesthetic regimes for each fish species is important. This article reviews the main anaesthetic and analgesic agents used in adult fish in a research setting.

Full-length and a smaller globular fragment of adiponectin have opposite roles in regulating monocyte/macrophage functions in ayu, Plecoglossus altivelis

Adiponectin (ADP), a regulator of the innate immune system, plays a role in the progression of inflammation and metabolic disorders in mammals. However, the role of ADP in fish is poorly understood. Here, we cloned the cDNA sequence of a ADP homolog (PaADP) gene from ayu. Multiple sequence alignment revealed that PaADP presented typical characteristics of ADPs. Phylogenetic tree analysis showed that PaADP was most closely related to that of rainbow trout. In healthy ayu, the transcripts of PaADP were detected in most of the tested tissues and cells, with the highest level in the adipose tissue. Upon V. anguillarum infection, the mRNA expression of PaADP was significantly up-regulated in the tissues and cells except adipose tissue. Subsequently, the full-length mature PaADP (fPaADP) and the globular domain fragment (gPaADP) were prokaryotically expressed in bacteria and purified, and anti-PaADP antibodies were produced. Western blot analysis revealed that three fragments including fPaADP and gPaADP were existed in ayu serum. The recombinant fPaADP (rfPaADP) had an anti-inflammatory effect on ayu MO/MФ by upregulating anti-inflammatory cytokine expressions, downregulating pro-inflammatory cytokine expressions, inhibiting the phagocytosis and subsequent bacterial killing. In contrast, the recombinant gPaADP (rgPaADP) presented a pro-inflammatory effect on ayu MO/MФ by upregulating pro-inflammatory cytokine expression, downregulating anti-inflammatory cytokine expressions, enhancing the phagocytosis and subsequent bacterial killing. These results suggested that fPaADP and gPaADP have opposite roles in the regulation of MO/MФ functions in ayu.

Molecular characterization of a tissue factor gene from ayu: A pro-inflammatory mediator via regulating monocytes/macrophages

Tissue factor (TF) plays an important role in the host's immune system as the principal initiator of coagulation. However, the precise function of TF in teleosts remains unclear. We determined the cDNA sequence of TF from ayu Plecoglossus altivelis (PaTF). The PaTF transcript was expressed in all tested tissues, and changes in expression were observed in tissues and monocytes/macrophages (MO/MФ) upon infection with Vibrio anguillarum. PaTF was prokaryotically expressed and purified to prepare anti-PaTF antibodies. Western blot analysis revealed that native PaTF was glycosylated in thrombocytes, but not in ayu MO/MФ. Microparticles could transfer PaTF to thrombocytes. PaTF neutralization or knockdown led to anti-inflammatory status in ayu MO/MФ upon V. anguillarum infection. PaTF neutralization reduced the apoptosis of ayu MO/MФ and improve survival rate in V. anguillarum-infected ayu. Our results indicate that PaTF plays a role in ayu immune response against bacterial infection as a pro-inflammatory mediator.

Impacts of Low Temperature on the Teleost Immune System

As poikilothermic vertebrates, fish can experience changes in water temperature, and hence body temperature, as a result of seasonal changes, migration, or efflux of large quantities of effluent into a body of water. Temperature shifts outside of the optimal temperature range for an individual fish species can have negative impacts on the physiology of the animal, including the immune system. As a result, acute or chronic exposure to suboptimal temperatures can impair an organisms' ability to defend against pathogens and thus compromise the overall health of the animal. This review focuses on the advances made towards understanding the impacts of suboptimal temperature on the soluble and cellular mediators of the innate and adaptive immune systems of fishes. Although cold stress can result in varying effects in different fish species, acute and chronic suboptimal temperature exposure generally yield suppressive effects, particularly on adaptive immunity. Knowledge of the effects of environmental temperature on fish species is critical for both the optimal management of wild species and the best management practices for aquaculture species.

CXCR3.1 and CXCR3.2 Differentially Contribute to Macrophage Polarization in Teleost Fish

The study of multiple copies of chemokine receptor genes in various teleosts has long appealed to investigators seeking to understand the evolution of the immune system. The CXCR CXCR3 gene has two isoforms, CXCR3.1 and CXCR3.2, which are both expressed in macrophages. The distinct roles of teleost CXCR3s have not been identified previously. In this article, we found that CXCR3.1 and CXCR3.2 differentially contributed to macrophage polarization in the teleosts: ayu (Plecoglossus altivelis), grass carp (Ctenopharyngodon idella), and spotted green pufferfish (Tetraodon nigroviridis). In ayu macrophages, the P. altivelis CXCR3.1 (PaCXCR3.1) gene was constitutively expressed, whereas the P. altivelis CXCR3.2 (PaCXCR3.2) gene was induced postinfection with Escherichia coli Upon E. coli infection, PaCXCR3.1⁺ and PaCXCR3.2⁺ macrophages showed an M1 and an M2 phenotype, respectively. CXCL9-11-like proteins mediated M1 and M2 polarization by interacting with the PaCXCR3.1 and PaCXCR3.2 proteins on macrophages, respectively. The transcription factors P. altivelis STAT1 and P. altivelis STAT3 were activated in PaCXCR3.1⁺ and PaCXCR3.2⁺ macrophages, respectively. Furthermore, the prognosis of septic ayu adoptively transferred with PaCXCR3.2⁺ macrophages was improved. Our data reveal a previously unknown mechanism for macrophage polarization, suggesting that redundant genes may regulate crucial functions in the teleost immune system.

Mobilisation and dysfunction of haematopoietic stem/progenitor cells after Listonella anguillarum infection in ayu, Plecoglossus altivelis

Haematopoietic stem/progenitor cells (HSPCs) can mobilise into blood and produce immune cell lineages following stress. However, the homeostasis and function of HSPCs after infection in teleosts are less well known. Here, we report that Listonella anguillarum infection enhances HSPC mobilisation and reduces their differentiation into myeloid cells in ayu (Plecoglossus altivelis), an aquacultured teleost in East Asia. We established a colony-forming unit culture (CFU-C) assay to measure HSPCs using conditioned medium from peripheral blood mononuclear cells stimulated with phytohaemagglutinin. The number of CFU-Cs decreased in the head kidney and increased in the blood and spleen of ayu infected with L. anguillarum. HSPC mobilisation after L. anguillarum infection was mediated by norepinephrine. Furthermore, HSPCs from ayu treated with L. anguillarum lipopolysaccharide (LPS) showed defective myeloid differentiation and could no longer rescue L. anguillarum-infected ayu. HSPC expansion was suppressed after L. anguillarum infection or its LPS treatment in vitro. These results reveal a link between HSPC regulation and pathogen infection in teleosts.