Characterization of the leukemia inhibitory factor receptor in the goldfish (Carassius auratus)

The goldfish primary kidney macrophage system

Miodrag (Mike) Belosevic and collaborators profoundly influenced the development of primary kidney macrophage culturing system (PKM) to study fish immunology in various aspects of comparative immunology. Their application of using PKM model, opened a new path for studying the development of macrophages, regulation of hematopoiesis, and cell specific response against various pathogens. By measuring histopathological and immunological outcomes, the biological implications of a variety of cytokines and signal transduction molecules could be elucidated with the established PKM system. A variety of growth factors mediating hematopoiesis and cytokines regulating the immune responses were functionally characterized, which served as a fundamental basis for making goldfish an excellent model to study fish immunology. Specifically, using in vivo and PKM based in vitro assays, the Belosevic lab advanced the goldfish-M. marinum model to study the anti-mycobacteria responses in teleosts, thus paving a way for the development of novel therapeutic approaches which could be applied in aquaculture settings or utilized as a model for human disease. In this review, we will look at the contribution of Dr. Mike Belosevic to teleost macrophage development, multiple cytokine functional characterization, and host-pathogen interactions.

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

The process of myeloid cell development (myelopoiesis) in fish has mainly been studied in three cyprinid species: zebrafish (Danio rerio), ginbuna carp (Carassius auratus langsdorfii) and goldfish (C. auratus, L.). Our studies on goldfish myelopoiesis have utilized in vitro generated primary kidney macrophage (PKM) cultures and isolated primary kidney neutrophils (PKNs) cultured overnight to study the process of macrophage (monopoiesis) and neutrophil (granulopoiesis) development and the key growth factors, receptors, and transcription factors that govern this process in vitro. The PKM culture system is unique in that all three subpopulations of macrophage development, namely progenitor cells, monocytes, and mature macrophages, are simultaneously present in culture unlike mammalian systems, allowing for the elucidation of the complex mixture of cytokines that regulate progressive and selective macrophage development from progenitor cells to fully functional mature macrophages in vitro. Furthermore, we have been able to extend our investigations to include the development of erythrocytes (erythropoiesis) and thrombocytes (thrombopoiesis) through studies focusing on the progenitor cell population isolated from the goldfish kidney. Herein, we review the in vitro goldfish model systems focusing on the characteristics of cell sub-populations, growth factors and their receptors, and transcription factors that regulate goldfish myelopoiesis.

Recombinant goldfish thrombopoietin up-regulates expression of genes involved in thrombocyte development and synergizes with kit ligand A to promote progenitor cell proliferation and colony formation

Thrombopoietin (TPO) is the principal regulator of thrombopoiesis and promotes the proliferation, differentiation and maturation of megakaryocytic progenitor cells in mammals. In this study we report on the molecular and functional characterization of goldfish TPO. Quantitative expression analysis of goldfish tpo revealed the highest mRNA levels in heart, followed by spleen, liver, brain, intestine and kidney tissues. Significant decrease of tpo and c-mpl expressions in goldfish primary kidney macrophage (PKM) cultures, as progenitor to macrophage development progressed, indicates that TPO is not involved in monopoiesis. Recombinant goldfish TPO (rgTPO) alone did not induce significant proliferation of progenitor cells, but TPO in cooperation with recombinant goldfish kit ligand A (rgKITLA) supported proliferation of progenitor cells in a dose-dependent manner. In response to rgTPO or a combination of rgTPO and rgKITLA, the mRNA levels of thrombopoietic markers cd41 and c-mpl as well as thrombo/erythropoietic transcription factors gata1 and lmo2 in sorted progenitor cells were up-regulated, while the mRNA levels of granulopoietic markers (cebpα and gcsfr) and the lymphoid transcription factor gata3 were down-regulated. Furthermore, rgTPO and rgKITLA synergistically stimulated thrombocytic colony-formation. Our results demonstrate that goldfish TPO has similar functions to mammalian TPO as a regulator of thrombopoiesis, and suggests a highly conserved molecular mechanism of thrombocyte development throughout evolution of vertebrates.

Cytokine gene expression and prostaglandin production in head kidney leukocytes isolated from Atlantic cod (Gadus morhua) added different levels of arachidonic acid and eicosapentaenoic acid

Primary head kidney leukocytes from Atlantic cod were isolated to evaluate the use of arachidonic acid and eicosapentaenoic acid by cyclooxygenases and the production of prostaglandins E₂ and E₃. The expression of cyclooxygenase genes and selected interleukin genes like Interleukin 1β, Interleukin 6, interleukin 8 and interleukin 10 were monitored. Increasing concentrations of eicosapentaenoic acid and arachidonic acid in equal amounts increased cyclooxygenase2 transcription as well as cell secretion of prostaglandin E₂. Even though the ratio of the two fatty acids was 1:1, the ratio between prostaglandin E₂ and E₃ was 50:1. The addition of arachidonic acid alone increased prostaglandin E₂ secretion but did not induce cyclooxygenase2 transcription. However, when the concentration of eicosapentaenoic acid was increased, maintaining arachidonic acid constant, both prostaglandin E₃ and prostaglandin E₂ production was induced and the prostaglandin E₂ production was higher than in cell cultures only added arachidonic acid. An up-regulation of cyclooxygenase2 transcription was also observed. The addition of the two fatty acids also affected the immune response by alteration of leukocytic cytokines gene expression. According to our results the Cyclooxygenase in cod seem to prefer arachidonic acid as substrate. Therefore, we suggest that the shift from marine oils (rich in n-3 fatty acids) to plant oils (higher in n-6 fatty acids) in the diet of commercially reared Atlantic cod could have negative effects on the whole organism through the increase in the production of prostaglandins belonging to those derived from n-6 fatty acids.

Molecular and functional characterization of kita and kitla of the goldfish (Carassius auratus L.)

Kit ligand and its type III tyrosine kinase receptor Kit promotes the survival, proliferation and differentiation of progenitor cells involved in mammalian myelopoiesis. In this study we report on the molecular and functional characterization of kit receptor A (kita) and kit ligand A (kitla) from the goldfish. Both kita and kitla were ubiquitously expressed in goldfish tissues, with higher mRNA levels observed in the kidney and spleen, the major hematopoietic organs of fish. Furthermore, both kita and kitla expressions decreased in a time-dependent manner in goldfish primary kidney macrophage (PKM) cultures, as progenitor to macrophage development progressed, and the highest expressions of both the receptor and ligand were observed in sorted progenitor cell populations. Activation of mature macrophage cultures increased both kita and kitla expressions. Kit ligand A induced chemotactic response, proliferation and survival of PKM cells in a dose-dependent manner, but did not induce differentiation of early PKM cells. These results are consistent with the role of kita and kitla during myelopoiesis of higher vertebrates and suggest a conserved mechanism of macrophage development throughout vertebrates.

Development of macrophages of cyprinid fish

The innate immune responses of early vertebrates, such as bony fishes, play a central role in host defence against infectious diseases and one of the most important effector cells of innate immunity are macrophages. In order for macrophages to be effective in host defence they must be present at all times in the tissues of their host and importantly, the host must be capable of rapidly increasing macrophage numbers during times of need. Hematopoiesis is a process of formation and development of mature blood cells, including macrophages. Hematopoiesis is controlled by soluble factors known as cytokines, that influence changes in transcription factors within the target cells, resulting in cell fate changes and the final development of specific effector cells. The processes involved in macrophage development have been largely derived from mammalian model organisms. However, recent advancements have been made in the understanding of macrophage development in bony fish, a group of organisms that rely heavily on their innate immune defences. Our understanding of the growth factors involved in teleost macrophage development, as well as the receptors and regulatory mechanisms in place to control them has increased substantially. Furthermore, model organisms such as the zebrafish have emerged as important instruments in furthering our understanding of the transcriptional control of cell development in fish as well as in mammals. This review highlights the recent advancements in our understanding of teleost macrophage development. We focused on the growth factors identified to be important in the regulation of macrophage development from a progenitor cell into a functional macrophage and discuss the important transcription factors that have been identified to function in teleost hematopoiesis. We also describe the findings of in vivo studies that have reinforced observations made in vitro and have greatly improved the relevance and importance of using teleost fish as model organisms for studying developmental processes.

Growth Factors of Lower Vertebrates

Colony-stimulating factor-1 (CSF-1) regulates mononuclear cell proliferation, differentiation, and survival. The functions of CSF-1 are well documented in mammals; however, little is known about CSF-1 biology in lower vertebrates. This is the first report on the identification and functional characterization of a fish CSF-1 molecule expressed highly in the spleen and in phorbol 12-myristate 13-acetate-stimulated monocytes. Goldfish CSF-1 is a 199-amino acid protein that possesses the required cysteine residues to form important intra-chain and inter-chain disulfide bonds that allow CSF-1 to form a functional homodimer and to interact with its high affinity receptor, CSF-1R. Recombinant goldfish CSF-1 formed a homodimer and bound to the soluble goldfish CSF-1R. The addition of the recombinant CSF-1 to sorted goldfish progenitor cells, monocytes, and macrophages induced the differentiation of monocytes into macrophages and the proliferation of monocyte-like cells. The proliferation of these cells was abrogated by addition of an anti-CSF-1R antibody as well as the soluble CSF-1R. The ability of the soluble CSF-1R to inhibit CSF-1-induced proliferation represents a novel mechanism for the regulation of CSF-1 function.

Analysis of leukemia inhibitory factor and leukemia inhibitory factor receptor in embryonic and adult zebrafish (Danio rerio)

Leukemia inhibitory factor (LIF) is a member of the IL-6 cytokine family that functions in the survival, repair and formation of neurons as well as in the maintenance of neural and embryonic stem cells. The functions of LIF have been well documented in mammals, however until recently, the presence of IL-6 family cytokines in ectothermic vertebrates has only been speculated. We report on the identification of lif and lifr transcripts in the zebrafish and document the expression of these molecules in the developing embryos and tissues of adult zebrafish. We also examined the phylogenetic relationship between these molecules and other IL-6 cytokine family members known in mammals. In adult zebrafish, lif is expressed in the kidney and brain while lifr is expressed in the kidney, gill, brain, spleen and liver. During zebrafish embryogenesis, lif and lifr are both expressed as early as 12 hours postfertilization (hpf). In developing zebrafish, lif is expressed in the otic vesicle, retina and cranial sensory ganglia, and lifr is strongly expressed in the notochord, forebrain, otic vesicle, cranial ganglia and the retina. Morpholino knockdown of Lif and Lifr in developing embryos suggests that Lifr, but not Lif is required for proper neural development. lifr morpholino-injected embryos exhibit defects in the trigeminal, facial and vagal branchiomotor neurons, and improper axonal development as measured by acetylated tubulin staining. These embryos also display severe hydrocephaly by 48 hpf. This suggests that Lifrs are involved in proper neural development in zebrafish. This is the first evidence of the expression and role of an LIFR-like molecule in developing fish.

A novel type-1 cytokine receptor from fish involved in the Janus kinase/Signal transducers and activators of transcription (Jak/STAT) signal pathway

Type I cytokine receptors mediate the action of the members of the long chain cytokines canonically involved in numerous physiological function. Here we report a novel cytokine receptor termed Japanese flounder glycoprotein 130 homologue or JfGPH, exhibiting the unique type I cytokine receptor motifs i.e. having a cytokine binding domain (CBD) containing two pairs of conserved cysteine (C) residues, a WSXWS motif, three fibronectin domains all in the extracellular region. It is also composed of the Jak binding domains Box 1 and Box 2, and a STAT 3 binding motif (Box 3) in the cytoplasmic region suggesting its mediatory role for Janus kinase/Signal transducers and activators of transcription (Jak/STAT) signal pathway. The JfGPH cDNA is about 3kb encoding 801 amino acid residues with a predicted molecular weight of 90kDa and its gene has an 11-exon/10-intron architecture. While JfGPH shows significant homology with the members of type-1 cytokine receptor family including IL6ST (or gp130), IL31alpha (or GLMR), CSF3R (or GCSFR), LIFR, OSMR, IL12Rbeta1 and LEPR, structural and phylogenetic analysis of its protein revealed that it is a novel and an ancestral cytokine receptor found in teleost. JfGPH gene is ubiquitously expressed in Japanese flounder tissues and in a natural embryo (HINAE) cell line showing its critical role in teleost physiological functions similar to gp130 in higher vertebrates. High expression of JfGPH transcripts in immune-related tissues and, in ovary and embryo-derived cell line suggest its role in immune responses, and reproduction/development, respectively. In vitro stimulation of spleen, kidney, peripheral blood leukocytes (PBLs) and HINAE revealed that JfGPH is down-regulated by polyinosinic:polycytidylic acid (poly I:C), an interferon (IFN) inducer, suggesting an apparent control of the JfGPH's expression during IFN-induced Jak/STAT signaling.

Interleukin-6 family cytokine M17 induces differentiation and nitric oxide response of goldfish (Carassius auratus L.) macrophages

Cytokines belonging to the interleukin-6 (IL-6) family function in many biological processes and display a high degree of redundancy within the family. Although a number of mRNA transcripts from teleost fish that resemble IL-6 family cytokines have been identified none have been functionally characterized to confirm their identity. We report on the identification and functional characterization of goldfish M17, a molecule possessing sequence and mRNA expression patterns similar to the mammalian and avian ciliary neurotrophic factor and mammalian leukemia inhibitory factor. Goldfish M17 was found to induce the production of nitric oxide in goldfish macrophages and stimulate the proliferation of macrophage progenitor cells when added in combination with cell-conditioned medium. Moreover, goldfish M17 was found to facilitate the differentiation of sorted monocytes into macrophages at biologically relevant concentrations.