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

Trypanosoma carassii infection in goldfish (Carassius auratus L.): changes in the expression of erythropoiesis and anemia regulatory genes

Trypanosoma carassii is a flagellated bloodstream parasite of cyprinid fish with pathogenesis manifesting primarily as anemia in experimentally infected fish. This anemia is characterized by decreases in the number of circulating red blood cells (RBCs) during peak parasitemia. We examined changes in the key blood metrics and expression of genes known to be important in the regulation of erythropoiesis. Increasing parasitemia was strongly correlated with an overall decrease in the total number of circulating RBCs. Gene expression of key erythropoiesis regulators (EPO, EPOR, GATA1, Lmo2, and HIFα) and proinflammatory cytokines (IFNγ and TNFα) were measured and their expressions differed from those in fish made anemic by injections of phenylhydrazine (PHZ). Significant upregulation of pro-erythropoietic genes was observed in PHZ-induced anemia, but not during peak parasitic infection. Previously, we reported on functional characterization of goldfish erythropoietin (rgEPO) and its ability to induce survival and differentiation of erythroid progenitor cells in vitro. Treatment of goldfish during the infection with rgEPO reduced the severity of anemia but failed to fully prevent the onset of the anemic state in infected fish. Proinflammatory cytokines have been implicated in the suppression of erythropoiesis during trypanosomiasis, specifically the cytokines TNFα, IFNγ, and IL-1β. Analysis of key proinflammatory cytokines revealed that mRNA levels of IFNγ and TNFα were upregulated in response to infection, but only TNFα increased in response to PHZ treatment. Synergistic activity of the proinflammatory cytokines may be required to sustain prolonged anemia. These findings provide insight into the relationship between T. carassii and host anemia and suggest that T. carassii may directly or indirectly suppress host erythropoiesis.

Selenium deficiency impaired immune function of the immune organs in young grass carp (Ctenopharyngodon idella)

This study aimed to investigate the effects of dietary selenium on resistance to skin haemorrhages and lesions and on immune function as well as the underlying mechanisms of those effects in the head kidney, spleen and skin of young grass carp (Ctenopharyngodon idella). A total of 540 healthy grass carp with initial body weight (226.48 ± 0.68 g) were randomly divided into six groups and fed six separate diets with graded dietary levels of selenium (0.025, 0.216, 0.387, 0.579, 0.795 and 1.049 mg/kg diet) for 80 days. After the feeding period, an immunization trial was performed by infection with Aeromonas hydrophila for 14 days. The results showed that, compared with the optimal selenium level, (1) selenium deficiency impaired the production of antibacterial compounds and immunoglobulins and down-regulated the transcript abundances of antimicrobial peptides and selenoproteins; (2) selenium deficiency aggravated inflammatory responses in part by up-regulating pro-inflammatory cytokines and down-regulating anti-inflammatory cytokines mRNA levels, which were partially related to [IKKα, β, γ/IκBα/NF-κB] signalling and [TOR/(S6K1, 4E-BP1)] signalling, respectively. Interestingly, selenium deficiency had no effect on the expression of TGF-β2, IL-4/13B, IL-10, IL-12p35, IL-15 (skin only) or 4E-BP2 in the head kidney, spleen and skin of young grass carp. Finally, based on the percent weight gain (PWG), the morbidity of skin haemorrhages and lesions, the ACP activity in the head kidney and the lysozyme activity in spleen, the optimal dietary selenium requirements for young grass carp were estimated to be 0.546-0.604 mg/kg diet. In summary, selenium deficiency decreased the growth performance and impaired the immune function in the head kidney, spleen and skin of young grass carp.

The impaired immune function and structural integrity by dietary iron deficiency or excess in gill of fish after infection with Flavobacterium columnare: Regulation of NF-κB, TOR, JNK, p38MAPK, Nrf2 and MLCK signalling

The aim of this study was to investigate the effects and potential mechanisms of dietary iron on immune function and structural integrity in gill of young grass carp (Ctenopharyngodon idella). A total of 630 grass carp (242.32 ± 0.58 g) were fed diets containing graded levels of iron at 12.15 (basal diet), 35.38, 63.47, 86.43, 111.09, 136.37 and 73.50 mg/kg for 60 days. Subsequently, a challenge test was conducted by infection with Flavobacterium columnare to investigate the effects of dietary iron on gill immune function and structural integrity in young grass carp. First, the results indicated that compared with the optimal iron level, iron deficiency decreased lysozyme (LZ) and acid phosphatase (ACP) activities, complement 3 (C3), C4 and immunoglobulin M (IgM) contents, and down-regulated the mRNA levels of antibacterial peptides, anti-inflammatory cytokines (except IL-4/13B), inhibitor of κBα (IκBα), target of rapamycin (TOR) and ribosomal protein S6 kinase 1 (S6K1). In contrast, iron deficiency up-regulated the mRNA levels of pro-inflammatory cytokines (except IL-6 and IFN-γ2), nuclear factor κB p65 (NF-κBp65), IκB kinases α (IKK), IKKβ, IKKγ, eIF4E-binding protein 1 (4E-BP1) and 4E-BP2 in gill of young grass carp, indicating that iron deficiency could impair immune function in fish gill. Second, iron deficiency down-regulated the mRNA levels of inhibitor of apoptosis protein (IAP) and myeloid cell leukemia 1 (Mcl-1), decreased activities and mRNA levels of antioxidant enzymes, down-regulated the mRNA levels of NF-E2-related factor 2 (Nrf2) and tight junction proteins (except claudin-12 and -15), and simultaneously increased malondialdehyde (MDA), protein carbonyl (PC) and reactive oxygen species (ROS) contents. Iron deficiency also up-regulated mRNA levels of cysteinyl aspartic acid-protease (caspase) -2, -7, -8, -9, Fas ligand (FasL), apoptotic protease activating factor-1 (Apaf-1), B-cell-lymphoma-2 associated X protein (Bax), p38 mitogen-activated protein kinase (p38MAPK), Kelch-like ECH-associating protein (Keap) 1a, Keap1b, claudin-12, -15 and MLCK, indicating that iron deficiency could disturb the structural integrity of gill in fish. Third, iron excess impaired immune function and structural integrity in gill of young grass carp. Forth, there was a better effect of ferrous fumarate than ferrous sulfate in young grass carp. Finally, the iron requirements based on ability against gill rot, ACP activity and MDA content in gill of young grass carp were estimated to be 76.52, 80.43 and 83.17 mg/kg, respectively.

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.

Environmentally induced tissue responses of hematopoietic system in abu mullet (Liza abu) and tiger tooth croaker (Otolithes ruber) from the Persian Gulf

The present investigation aimed to assess the possibility of using plasma levels of erythropoietin (EPO) hormone and tissue changes of hematopoietic organs as biomarkers of environmental pollution in abu mullet (Liza abu) and tiger tooth croaker (Otolithes ruber) collected from Musa Creek (northwest of the Persian Gulf). 120 L. abu and O. ruber were collected from five stations at the Musa Creek: Petrochemical, Ghanam, Doragh, Zangi and Patil stations. Blood samples were obtained from the caudal vein. Tissue samples were also taken from the spleen and head kidney, and tissue sections were prepared according to routine histological methods. The concentrations of Hg, Pb, Zn, Cu, and Cd were also measured in the sediment samples. The minimum level of EPO and the most severe tissue changes were determined in fish collected near a Petrochemical station. This station is adjacent to the Imam Khomeini Petrochemical Complex and receives highly contaminated effluents from this complex. The highest degree of contamination (C_d) also belonged to this station. The fish collected from the Patil station represented the highest EPO level and the least tissue changes. This station exhibited a lesser degree of contamination. Based on the results, there was a significant correlation between the plasma level of EPO hormone and the degree of environmental contamination.

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.

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.

Analysis of the erythropoietin of a Tibetan Plateau schizothoracine fish (Gymnocypris dobula) reveals enhanced cytoprotection function in hypoxic environments

BACKGROUND

Erythropoietin (EPO) is a glycoprotein hormone that plays a principal regulatory role in erythropoiesis and initiates cell homeostatic responses to environmental challenges. The Qinghai-Tibet Plateau is a natural laboratory for hypoxia adaptation. Gymnocypris dobula is a highly specialized plateau schizothoracine fish that is restricted to > 4500 m high-altitude freshwater rivers and ponds in the Qinghai-Tibet Plateau. The role of EPO in the adaptation of schizothoracine fish to hypoxia is unknown.

RESULTS

The EPO and EPO receptor genes from G. dobula and four other schizothoracine fish from various altitudinal habitats were characterized. Schizothoracine EPOs are predicted to possess 2-3 N-glycosylation (NGS) sites, 4-5 casein kinase II phosphorylation (CK2) sites, 1-2 protein kinase C (PKC) phosphorylation sites, and four conserved cysteine residues within four helical domains, with variations in the numbers of NGS and CK2 sites in G. dobula. PAML analysis indicated a d N/d S value (ω) = 1.112 in the G. dobula lineage, and a few amino acids potentially under lineage-specific positive selection were detected within the G. dobula EPO. Similarly, EPO receptors of the two high-altitude schizothoracines (G. dobula and Ptychobarbus kaznakovi), were found to be statistically on the border of positive selection using the branch-site model (P-value = 0.096), and some amino acids located in the ligand-binding domain and the fibronectin type III domain were identified as potentially positive selection sites. Tissue EPO expression profiling based on transcriptome sequencing of three schizothoracines (G. dobula, Schizothorax nukiangensis Tsao, and Schizothorax prenanti) showed significant upregulation of EPO expression in the brain and less significantly in the gill of G. dobula. The elevated expression together with the rapid evolution of the EPO gene in G. dobula suggested a possible role for EPO in adaptation to hypoxia. To test this hypothesis, Gd-EPO and Sp-EPO were cloned into an expression vector and transfected into the cultured cell line 293 T. Significantly higher cell viability was observed in cells transfected with Gd-EPO than cells harboring Sp-EPO when challenged by hypoxia.

CONCLUSION

The deduced EPO proteins of the schizothoracine fish contain characteristic structures and important domains similar to EPOs from other taxa. The presence of potentially positive selection sites in both EPO and EPOR in G. dobula suggest possible adaptive evolution in the ligand-receptor binding activity of the EPO signaling cascade in G. dobula. Functional study indicated that the EPO from high-altitude schizothoracine species demonstrated features of hypoxic adaptation by reducing toxic effects or improving cell survival when expressed in cultured cells, providing evidence of molecular adaptation to hypoxic conditions in the Qinghai-Tibet Plateau.

Exploring erythropoiesis of common carp (Cyprinus carpio) using an in vitro colony assay in the presence of recombinant carp kit ligand A and erythropoietin

The use of in vitro colony assays in mammals has contributed to identification of erythroid progenitor cells such as burst-forming unit-erythroid (BFU-E) and colony-forming unit-erythroid (CFU-E) progenitors, and serves to examine functions of erythropoietic growth factors like Erythropoietin (Epo) and Kit ligand. Here, we established an in vitro colony-forming assay capable of investigating erythropoiesis in carp (Cyprinus carpio), cloned and functionally characterized recombinant homologous molecules Epo and Kit ligand A (Kitla), and identified three distinct erythroid progenitor cells in carp. Recombinant carp Epo induced the formation of CFU-E-like and BFU-E-like erythroid colonies, expressing erythroid marker genes, β-globin, epor and gata1. Recombinant carp Kitla alone induced limited colony formation, whereas a combination of Kitla and Epo dramatically enhanced erythroid colony formation and colony cell growth, as well as stimulated the formation of thrombocytic/erythroid colonies expressing not only erythroid markers but also thrombocytic markers, cd41 and c-mpl. Utilizing this colony assay to examine the distribution of distinct erythroid progenitor cells in carp, we demonstrated that carp head and trunk kidney play a primary role in erythropoiesis, while the spleen plays a secondary. Furthermore, we showed that presumably bi-potent thrombocytic/erythroid progenitor cells localize principally in the trunk kidney. Our results indicate that teleost fish possess mechanisms of Epo- and Kitla-dependent erythropoiesis similar to those in other vertebrates, and also help to demonstrate the diversity of erythropoietic sites among vertebrates.

Application of biomarkers in Epaulet grouper (Epinephelus stoliczkae) to assess chromium pollution in the Chabahar Bay and Gulf of Oman

In the present study plasma levels of erythropoietin (EPO) hormone and kidney histological changes were assessed as biomarkers to evaluate the chromium pollution in Epaulet grouper (Epinephelus stoliczkae) obtained from different areas in Chabahar Bay and Gulf of Oman. Chemical analyses included the evaluation of chromium in the fish kidney tissue and sediment. The highest and lowest concentrations of chromium were measured in the kidney of fish and sediment collected from Konarak (47.53±1.23 and 110±1.4 μg g(-1)) and the mouth of Chabahar Bay (3.43±1.31 and 13.5±3.23 μg g(-1)), respectively. There was significant difference (P<0.05) of EPO plasma levels between Konarak, Beris and Ramin stations with the mouth of Chabahar Bay as the cleanest station. Reduction of Bowman's space, occlusion of the tubule lumen, leukocytes infiltration, melanomacrophage centers aggregation, nuclear vacuolation, nuclei hypertrophy of tubule cells, necrosis of the tubules, lifting of the tubular basement membrane and dilatation of glomerular capillaries were the most alterations observed in the kidney. The HAI values of Epaulet grouper from Konarak, Beris and Ramin stations were significantly higher than other stations (P<0.05). It was concluded that selected biomarkers as a first investigation could be useful tools to environmental biomonitoring programs.

The influence of artificially introduced N-glycosylation sites on the in vitro activity of Xenopus laevis erythropoietin

Erythropoietin (EPO), the primary regulator of erythropoiesis, is a heavily glycosylated protein found in humans and several other mammals. Intriguingly, we have previously found that EPO in Xenopus laevis (xlEPO) has no N-glycosylation sites, and cross-reacts with the human EPO (huEPO) receptor despite low homology with huEPO. In this study, we introduced N-glycosylation sites into wild-type xlEPO at the positions homologous to those in huEPO, and tested whether the glycosylated mutein retained its biological activity. Seven xlEPO muteins, containing 1–3 additional N-linked carbohydrates at positions 24, 38, and/or 83, were expressed in COS-1 cells. The muteins exhibited lower secretion efficiency, higher hydrophilicity, and stronger acidic properties than the wild type. All muteins stimulated the proliferation of both cell lines, xlEPO receptor-expressing xlEPOR-FDC/P2 cells and huEPO receptor-expressing UT-7/EPO cells, in a dose-dependent manner. Thus, the muteins retained their in vitro biological activities. The maximum effect on xlEPOR-FDC/P2 proliferation was decreased by the addition of N-linked carbohydrates, but that on UT-7/EPO proliferation was not changed, indicating that the muteins act as partial agonists to the xlEPO receptor, and near-full agonists to the huEPO receptor. Hence, the EPO-EPOR binding site in X. laevis locates the distal region of artificially introduced three N-glycosylation sites, demonstrating that the vital conformation to exert biological activity is conserved between humans and X. laevis, despite the low similarity in primary structures of EPO and EPOR.

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.

Molecular and functional characterization of erythropoietin receptor of the goldfish (Carassius auratus L.)

Erythropoietin receptor (EPOR) is a member of the class I cytokine receptor superfamily and signaling through this receptor is important for the proliferation, differentiation and survival of erythrocyte progenitor cells. This study reports on the molecular and functional characterization of goldfish EPOR. The identified goldfish EPOR sequence possesses the conserved EPOR ligand binding domain, the fibronectin domain, the class I cytokine receptor superfamily motif (WSXWS) as well as several intracellular signaling motifs characteristic of other vertebrate EPORs. The expression of epor mRNA in goldfish tissues, cell populations and cells treated with recombinant goldfish EPO (rgEPO) were evaluated by quantitative PCR revealing that goldfish epor mRNA is transcribed in both erythropoietic tissues (blood, kidney and spleen) and non-hematopoietic tissues (brain, heart and gill), as well as in immature erythrocytes. Recombinant goldfish EPOR (rgEPOR), consisting of its extracellular domain, dose-dependently inhibited proliferation of progenitor cells induced by rgEPO. In vitro binding studies indicated that rgEPO exists as monomer, dimer and/or trimmer and that rgEPOR exists as monomer and/or homodimer, and when incubated together, formed a ligand-receptor complex. Our results demonstrate that goldfish EPO/EPOR signaling has been highly conserved throughout vertebrate evolution as a required mechanism for erythrocyte development.

Expressions of transcription factors in goldfish (Carassius auratus L.) macrophages and their progenitors

The development of macrophages is a highly regulated process requiring coordination amongst transcription factors. The presence/absence, relative levels, antagonism, or synergy of all transcription factors involved is critical to directing lineage cell fate and differentiation. While relative levels of many key myeloid transcription factors have been determined in mammalian macrophage differentiation, a similar set of studies have yet to be conducted in a teleost system. In this study, we report on the mRNA levels of transcription factors (cebpa, cjun, cmyb, egr1, gata1, gata2, gata3, lmo2, mafb, pax5, pu.1 and runx1) in sorted goldfish progenitor cells, monocytes, and macrophages from primary kidney macrophage cultures. The mRNA levels of runx1 and pu.1 were significantly higher, gata3 and pax5 mRNA levels were lower, in monocytes compared to progenitors, and the mRNA levels of cjun, egr1, gata2, gata3, mafb and pax5 were significantly decreased in macrophages compared to progenitor cells. The relative mRNA levels of the interferon regulatory factor family of transcription factors, irf1, irf2, irf5, irf7, irf8 and irf9 in sorted progenitors, monocytes and macrophages were also measured. In contrast to other irf family transcription factors examined, irf8 mRNA levels were increased in monocytes compared to progenitors by greater than three-fold, suggesting that irf8 is important for monopoiesis. Lastly, we show the differential regulation of myeloid transcription factor mRNA levels in sorted progenitor cells from 1, 2, or 3-day old cultures in response to the recombinant goldfish growth factors, rgCSF-1 and rgKITLA.