Development of an Atlantic salmon heart endothelial cell line (ASHe) that responds to lysophosphatidic acid (LPA)

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.

Cell line derived from muscle of Gymnocypris przewalskii, a species of Schizothoracinae in Qinghai Lake, Qinghai-Tibet Plateau

Gymnocypris przewalskii (naked carp), a native teleost, plays an important role in the ecosystem of Qinghai Lake (altitude, 3.2 km) on the Qinghai-Tibet Plateau in China. We developed a new cell line from the muscle of G. przewalskii using the explant technique and named the cell line GPM. This cell line was maintained in DMEM medium (high glucose) supplemented with 15% fetal bovine serum (FBS). The cell line was successfully subcultured up to 32 passages and was authenticated by immunofluorescence assay, sequencing the mitochondrial cytochrome C oxidase subunit I (COI) and 16S rRNA genes, and by chromosome analysis. In the medium containing 15% FBS, the cell line could be passaged stably at 25 °C. The GPM cell line could express green fluorescent protein (GFP) with a CMV promoter with about 5% transfection efficiency. MTT tests showed that Clostridium botulinum toxin (BTX) was toxic to the cell line. The cell line could be successfully cryopreserved in liquid nitrogen with a revival efficiency of over 70%. This study demonstrated that the GPM cell line can be used as an important tool for understanding the physiological characteristics of G. przewalskii, and it can provide a resource for studying gene function and toxicological reactions in vitro.

Establishment of a cell line derived from the gills of Gymnocypris przewalskii, an endemic Schizothoracine fish from Qinghai Lake of Tibet Plateau

Gymnocypris przewalskii (Naked carp), a native teleost, plays an important role in maintaining the ecological balance of Lake Qinghai (altitude, 3.2 km), the largest saline lake in China. In this study, a new gill cell line from G. przewalskii was developed using the explant technique and named as GPG. This cell line was maintained in Dulbecco's Modified Eagle Medium (DMEM) (high glucose), supplemented with 15% fetal bovine serum (FBS), and was successfully subcultured up to 32 passages. Meanwhile, this cell line was also authenticated by sequencing the mitochondrial cytochrome C oxidase subunit I (COI) and 16S rRNA genes and by chromosome analysis. With the Cytomegalovirus (CMV) promoter, the GPG cell line could express green fluorescent protein (GFP) at about 5% transfection efficiency. MTT test showed that Clostridium botulinum toxin (BTX) was toxic to the cell line. After cryopreservation with 10% dimethyl sulfoxide (DMSO), this cell line could be successfully revived at an efficiency over 70%. This study revealed that the GPG cell line could be used as materials for physio-chemical investigation of G. przewalskii and also provided a tool for gene function study and toxicological reaction in vitro.

The sine qua non of the fish invitrome today and tomorrow in environmental radiobiology

Fish cell lines, collectively referred to as the fish invitrome, are useful diagnostic tools to study radiation impacts on aquatic health and elucidate radiation mechanisms in fish. This paper will highlight the advantages, discuss the challenges, and propose possible future directions for uses of the fish invitrome in the field of environmental radiobiology. The fish invitrome contains at least 714 fish cell lines. However, only a few of these cell lines have been used to study radiation biology in fish and they represent only 10 fish species. The fish invitrome is clearly not yet explored for its full potential in radiation biology. Evidence suggests that they are useful and, in some cases, irreplaceable in making underlying theories and fundamental concepts in radiation responses in fish. The debate of whether environmental radiation is harmful, presents risks, has no effect on health, or is beneficial is on-going and is one that fish cell lines can help address in a time-effective fashion. Any information obtained with fish cell lines is useful in the framework of environment radiation risk assessments. Radiation threats to aquatic health will continue due to the very likely rise of nuclear energy and medicine in the future. The fish invitrome, in theory, lives forever and can meet new challenges at any given time to provide diagnostic risk analyses pertaining to aquatic health and environmental radiation protection.

Improving a fish intestinal barrier model by combining two rainbow trout cell lines: epithelial RTgutGC and fibroblastic RTgutF

An in vitro model of the fish intestine is of interest for research and application in diverse fields such as fish physiology, aquaculture and chemical risk assessment. The recently developed epithelial barrier model of the fish intestine relies on the RTgutGC cell line from rainbow trout (Oncorhynchus mykiss), cultured in inserts on permeable membranes. Our aim was to extend the current system by introducing intestinal fibroblasts as supportive layer in order to reconstruct the epithelial-mesenchymal interface as found in vivo. We therefore initiated and characterized the first fibroblast cell line from the intestine of rainbow trout, which has been termed RTgutF. Co-culture studies of RTgutGC and RTgutF were performed on commercially available electric cell substrate for impedance sensing (ECIS) and on newly developed ultrathin, highly porous alumina membranes to imitate the cellular interaction with the basement membrane. Cellular events were examined with non-invasive impedance spectroscopy to distinguish between barrier tightness and cell density in the ECIS system and to determine transepithelial electrical resistance for cells cultured on the alumina membranes. We highlight the relevance of the piscine intestinal fibroblasts for an advanced intestinal barrier model, particularly on ultrathin alumina membranes. These membranes enable rapid crosstalk of cells cultured on opposite sides, which led to increased barrier tightening in the fish cell line-based epithelial-mesenchymal model.

The common field lampricide 3-trifluoromethyl-4-nitrophenol is a potential radiosensitizer in fish cells

PURPOSE

To evaluate if the common field lampricide 3-trifluoromethyl-4-nitrophenol (TFM) that is intended to eradicate the invasive species sea lampreys in the Great Lakes has the potential to sensitize radiation responses in cells from non-targeted native fish MATERIALS AND METHODS: The TFM toxicity was assessed acutely and chronically with the clonogenic fish cell line eelB. The acute toxicity (24-h exposure) was determined by the fluorescent cell viability probe Alamar Blue. The chronic toxicity was determined either by Alamar Blue (7-d exposure) or the clonogenic survival assay (14-d exposure). Pre- and post-exposure of fish cells to environmentally relevant TFM concentrations following gamma irradiation were performed. Clonogenic survival was determined to assess the damage level of radiation-induced reproductive cell death.

RESULTS

The chronic toxicity tests were more sensitive than the acute toxicity tests. The 14-d EC₅₀ using the clonogenic survival endpoint was 2.09 ± 0.28 μg/mL and was statistically similar to the 7-d EC₅₀ (1.85 ± 0.07 μg/mL) based on the Alamar Blue-based cytotoxicity endpoint. Post-exposure of cells to environmentally relevant TFM concentrations following irradiation did not have any effect as compared to the irradiation alone group. In contrast, pre-exposure of cells to TFM following irradiation had a negative additive effect when the total radiation dose was 2 Gy, but not 0.1 or 0.5 Gy.

CONCLUSION

Our results suggest that the common field lampricide TFM is a potential radiation sensitizer in cells from non-targeted native fish. This could be a health problem of concern for non-targeted native fish if a large accidental radioactive release occurs.

VER-155008 induced Hsp70 proteins expression in fish cell cultures while impeding replication of two RNA viruses

The heat-shock protein 70 (Hsp70) inhibitor, VER-155008 (VER), was explored as a potential antiviral agent for two RNA viruses important to fish aquaculture, viral hemorrhagic septicemia virus (VHSV) and infectious pancreatic necrosis virus (IPNV). Studies were done at a temperature of 14 °C, and with cell lines commonly used to propagate these viruses. These were respectively EPC from fathead minnow for VHSV and CHSE-214 from Chinook salmon embryo for IPNV. Additionally, both viruses were studied with the Atlantic salmon heart endothelial cell line ASHe. For both VHSV and IPNV, 25 μM VER impeded replication. This was evidenced by delays in the development of cytopathic effect (CPE) and the expression of viral proteins, N for VHSV and VP2 for IPNV, and by less production of viral RNA and of viral titre. As VER inhibits the activity of Hsp70 family members, these results suggest that VHSV and IPNV utilize one or more Hsp70s in their life cycles. Yet neither virus induced Hsp70. Surprisingly VER alone induced Hsp70, but whether this induction modulated VER's antiviral effects is unknown. Exploring this apparent paradox in the future should improve the usefulness of VER as an antiviral agent.

Transforming growth factor-β1 induces differentiation of rainbow trout (Oncorhynchus mykiss) cardiac fibroblasts into myofibroblasts

The collagen content of the rainbow trout heart increases in response to cold acclimation and decreases with acclimation to warm temperatures. This ability to remodel the myocardial extracellular matrix (ECM) makes these fish useful models to study the cellular pathways involved in collagen regulation in the vertebrate heart. Remodelling of the ECM in the mammalian heart is regulated, in part, by myofibroblasts which arise from pre-existing fibroblasts in response to transforming growth factor-β1 (TGF-β1). We have previously demonstrated that treatment of cultured rainbow trout cardiac fibroblasts with human TGF-β1 causes an increase in collagen production. Here, we showed that repetitive treatment of rainbow trout cardiac fibroblasts with a physiologically relevant concentration of human recombinant TGF-β1 results in a ∼29-fold increase in phosphorylated small mothers against decapentaplegic 2 (pSmad2); a 2.9-fold increase in vinculin protein, a 1.2-fold increase in cellular size and a 3-fold increase in filamentous actin (F-actin). These are common markers of the transition of fibroblasts to myofibroblasts. Cells treated with TGF-β1 also had highly organized cytoskeletal α-smooth muscle actin, as well as increased transcript abundances of mmp-9, timp-2 and col1a1 Furthermore, using gelatin zymography, we demonstrated that TGF-β1 treatment causes a 5.3-fold increase in gelatinase activity. Together, these results suggest that trout cardiac fibroblasts have the capacity to differentiate into myofibroblasts and that this cell type can increase extracellular collagen turnover via gelatinase activity. Cardiac myofibroblasts are, therefore, likely involved in the remodelling of the cardiac ECM in the trout heart during thermal acclimation.

Assessing off-target cytotoxicity of the field lampricide 3-trifluoromethyl-4-nitrophenol using novel lake sturgeon cell lines

Lampricides are currently being applied to streams and rivers to control the population of sea lamprey, an invasive species, in the Great Lakes. The most commonly used lampricide agent used in the field is 3-trifluoromethyl-4-nitrophenol (TFM), which targets larval sea lamprey in lamprey-infested rivers and streams. The specificity of TFM is due to the relative inability of sea lamprey to detoxify the agent relative to non-target fishes. There is increasing concern, however, about non-target effects on fishes, particularly threatened populations of juvenile lake sturgeon (LS; Acipenser fulvescens). There is therefore a need to develop models to better define lake sturgeon's response to TFM. Here we report the establishment of five LS cell lines derived from the liver, gill, skin and intestinal tract of juvenile LS and some of their cellular characteristics. All LS cell lines grew well at 25 °C in Leibovitz's (L)- 15 medium supplemented with 10% FBS. All cell lines demonstrated high senescence-associated β-galactosidase activity and varying levels of Periodic acid Schiff-positive polysaccharides, indicating substantial production of glycoproteins and mucosubstances by the cells. Comparative toxicity of TFM in the five LS cell lines was assessed by two fluorescent cell viability dyes, Alamar Blue and CFDA-AM, in conditions with and without serum and at 24 or 72 h exposure. Deduced EC₅₀ values were compared between the cell lines and to the reported in vivo LC₅₀s. Tissues sensitive to the effects of TFM in vivo correlated with cell lines from the same tissues being most sensitive to TFM in vitro. EC₅₀ values for the LSliver-e cells was significantly lower than the EC₅₀ for the rainbow trout (RBT) liver cells RTL-W1, reaffirming the in vivo observation that LS was generally more TFM-sensitive than rainbow trout. Our data suggests that whole-fish sensitivity of LS to TFM is likely attributable to sensitivity at the cellular level. Thus, LS cell lines, as well as those of RBT, can be used to screen and evaluate the toxicity of the next generation of lampricides on non-target fish such as lake sturgeon.

Atlantic salmon endothelial cells from the heart were more susceptible than fibroblasts from the bulbus arteriosus to four RNA viruses but protected from two viruses by dsRNA pretreatment

Heart diseases caused by viruses are major causes of Atlantic salmon aquaculture loss. Two Atlantic salmon cardiovascular cell lines, an endothelial cell line (ASHe) from the heart and a fibroblast cell line (BAASf) from the bulbus arteriosus, were evaluated for their response to four fish viruses, CSV, IPNV, VHSV IVa and VHSV IVb, and the innate immune agonist, double-stranded RNA mimic poly IC. All four viruses caused cytopathic effects in ASHe and BAASf. However, ASHe was more susceptible to all four viruses than BAASf. When comparing between the viruses, ASHe cells were found to be moderately susceptible to CSV and VHSV IVb, but highly susceptible to IPNV and VHSV IVa induced cell death. All four viruses were capable of propagating in the ASHe cell line, leading to increases in virus titre over time. In BAASf, CSV and IPNV produced more than one log increase in titre from initial infection, but VHSV IVb and IVa did not. When looking at the antiviral response of both cell lines, Mx proteins were induced in ASHe and BAASf by poly IC. All four viruses induced Mx proteins in BAASf, while only CSV and VHSV IVb induced Mx proteins in ASHe. IPNV and VHSV IVa suppressed Mx proteins expression in ASHe. Pretreatment of ASHe with poly IC to allow for Mx proteins accumulation protected the culture from subsequent infections with IPNV and VHSV IVa, resulting in delayed cell death, reduced virus titres and reduced viral proteins expression. These data suggest that endothelial cells potentially can serve as points of infections for viruses in the heart and that two of the four viruses, IPNV and VHSV IVa, have mechanisms to avoid or downregulate antiviral responses in ASHe cells. Furthermore, the high susceptibility of the ASHe cell line to IPNV and VHSV IVa can make it a useful tool for studying antiviral compounds against these viruses and for general detection of fish viruses.

Characterizing responses to gamma radiation by a highly clonogenic fish brain endothelial cell line

PURPOSE

The clonogenic property and radiobiological responses of a fish brain endothelial cell line, eelB, derived from the American eel were studied.

METHODS

Clonogenic assays were performed to determine the plating efficiency of the eelB cells and to evaluate the clonogenic survival fractions after direct irradiation to low-dose low-LET gamma radiation or receiving irradiated cell conditioned medium in the bystander effect experiments.

RESULT

eelB had the second highest plating efficiency ever reported to date for fish cell lines. Large eelB macroscopic colonies could be formed in a short period of time and were easy to identify and count. Unlike with other fish clonogenic cell lines, which had a relatively slow proliferation profile, clonogenic assays with the eelB cells could be completed as early as 12 days in culture. After direct irradiation with gamma rays at low doses ranging from 0.1Gy to 5Gy, the dose-clonogenic survival curve of the eelB cell line showed a linear trend and did not develop a shoulder region. A classical radio-adaptive response was not induced with the clonogenic survival endpoint when the priming dose (0.1 or 0.5Gy) was delivered 6h before the challenge dose (3 or 5Gy). However, a radio-adaptive response was observed in progeny cells that survived 5Gy and developed lethal mutations. eelB appeared to lack the ability to produce damaging radiation-induced bystander signals on both eelB and HaCaT recipient cells.

CONCLUSION

eelB cell line could be a very useful cell model in the study of radiation impacts on the aquatic health.