Cross-interference of two model peroxisome proliferators in peroxisomal and estrogenic pathways in brown trout hepatocytes

Effects of Benzo[k]fluoranthene at Two Temperatures on Viability, Structure, and Detoxification-Related Genes in Rainbow Trout RTL-W1 Cell Spheroids

Polycyclic aromatic hydrocarbons (PAHs) and global warming impact aquatic ecosystems, eventually interacting. Monolayer (2D) cultures of cell lines, such as the rainbow trout liver RTL-W1, are employed for unveiling toxicological effects in fish. Nonetheless, three-dimensional (3D) models constitute an alternate paradigm, better emulating in vivo responses. Here, ultra-low attachment (ULA) plates were used to generate ten-day-old RTL-W1 spheroids for exposure to a control, a solvent control (0.1% DMSO) and the model PAH benzo[k]fluoranthene (BkF) at 10 and 100 nM and at 18 and 23 °C (thermal stress). After a 4-day exposure, spheroids were analyzed for viability (alamarBlue and lactate dehydrogenase), biometry (area, diameter and sphericity), histocytology (optical and electron microscopy), and mRNA levels of the detoxification-related genes cytochrome P450 (CYP)1A, CYP3A27, aryl hydrocarbon receptor (AhR), glutathione S-transferase (GST), uridine diphosphate-glucuronosyltransferase (UGT), catalase (CAT), multidrug resistance-associated protein 2 (MRP2) and bile salt export protein (BSEP). Immunocytochemistry (ICC) was used to assess CYP1A protein expression. Neither temperature nor BkF exposure altered the spheroids' viability or biometry. BkF modified the cell's ultrastructure. The expression of CYP1A was augmented with both BkF concentrations, while AhR's increased at the higher concentration. The CYP1A protein showed a dose-dependent increase. Temperature and BkF concurrently modelled UGT's expression, which increased in the 100 nM condition at 23 °C. Conversely, CYP3A27, MRP2, and BSEP expressions lowered at 23 °C. CAT and GST mRNA levels were uninfluenced by either stressor. Overall, BkF and temperature impacted independently or interactively in RTL-W1 spheroids. These seem to be useful novel tools for studying the liver-related effects of temperature and PAHs.

17α-Ethynylestradiol and Levonorgestrel Exposure of Rainbow Trout RTL-W1 Cells at 18 °C and 21 °C Mainly Reveals Thermal Tolerance, Absence of Estrogenic Effects, and Progestin-Induced Upregulation of Detoxification Genes

Fish are exposed to increased water temperatures and aquatic pollutants, including endocrine-disrupting compounds (EDCs). Although each stressor can disturb fish liver metabolism independently, combined effects may exist. To unveil the molecular mechanisms behind the effects of EDCs and temperature, fish liver cell lines are potential models needing better characterisation. Accordingly, we exposed the rainbow trout RTL-W1 cells (72 h), at 18 °C and 21 °C, to ethynylestradiol (EE2), levonorgestrel (LNG), and a mixture of both hormones (MIX) at 10 µM. The gene expression of a selection of targets related to detoxification (CYP1A, CYP3A27, GST, UGT, CAT, and MRP2), estrogen exposure (ERα, VtgA), lipid metabolism (FAS, FABP1, FATP1), and temperature stress (HSP70b) was analysed by RT-qPCR. GST expression was higher after LNG exposure at 21 °C than at 18 °C. LNG further enhanced the expression of CAT, while both LNG and MIX increased the expressions of CYP3A27 and MRP2. In contrast, FAS expression only increased in MIX, compared to the control. ERα, VtgA, UGT, CYP1A, HSP70b, FABP1, and FATP1 expressions were not influenced by the temperature or the tested EDCs. The RTL-W1 model was unresponsive to EE2 alone, sensitive to LNG (in detoxification pathway genes), and mainly insensitive to the temperature range but had the potential to unveil specific interactions.

Estrogenic Responsiveness of Brown Trout Primary Hepatocyte Spheroids to Environmental Levels of 17α-Ethinylestradiol

Three-dimensional (3D) fish hepatocyte cultures are promising alternative models for replicating in vivo data. Few studies have attempted to characterise the structure and function of fish 3D liver models and illustrate their applicability. This study aimed to further characterise a previously established spheroid model obtained from juvenile brown trout (Salmo trutta) primary hepatocytes under estrogenic stimulation. The spheroids were exposed for six days to environmentally relevant concentrations of 17α-ethinylestradiol-EE2 (1-100 ng/L). The mRNA levels of peroxisome (catalase-Cat and urate oxidase-Uox), lipid metabolism (acyl-CoA long chain synthetase 1-Acsl1, apolipoprotein AI-ApoAI, and fatty acid binding protein 1-Fabp1), and estrogen-related (estrogen receptor α-ERα, estrogen receptor β-ERβ, vitellogenin A-VtgA, zona pellucida glycoprotein 2.5-ZP2.5, and zona pellucida glycoprotein 3a.2-ZP3a.2) target genes were evaluated by quantitative real-time polymerase chain reaction. Immunohistochemistry was used to assess Vtg and ZP protein expressions. At the highest EE2 concentration, VtgA and ZP2.5 genes were significantly upregulated. The remaining target genes were not significantly altered by EE2. Vtg and ZP immunostaining was consistently increased in spheroids exposed to 50 and 100 ng/L of EE2, whereas lower EE2 levels resulted in a weaker signal. EE2 did not induce significant changes in the spheroids' viability and morphological parameters. This study identified EE2 effects at environmentally relevant doses in trout liver spheroids, indicating its usefulness as a proxy for in vivo impacts of xenoestrogens.

Prolonged Cold Exposure Negatively Impacts Atlantic Salmon (Salmo salar) Liver Metabolism and Function

Large-scale mortality events have occurred during the winter in Atlantic salmon sea cages in Eastern Canada and Iceland. Thus, in salmon held at 3 °C that were apparently healthy (i.e., asymptomatic) and that had 'early' and 'advanced' symptoms of 'winter syndrome'/'winter disease' (WS/WD), we measured hepatic lipid classes and fatty acid levels, and the transcript expression of 34 molecular markers of fatty liver disease (FLD; a clinical sign of WS/WD). In addition, we correlated our results with previously reported characteristics associated with this disease's progression in these same individuals. Total lipid and triacylglycerol (TAG) levels increased by ~50%, and the expression of 32 of the 34 genes was dysregulated, in fish with symptoms of FLD. TAG was positively correlated with markers of inflammation (5loxa, saa5), hepatosomatic index (HSI), and plasma aspartate aminotransferase levels, but negatively correlated with genes related to lipid metabolism (elovl5b, fabp3a, cd36c), oxidative stress (catc), and growth (igf1). Multivariate analyses clearly showed that the three groups of fish were different, and that saa5 was the largest contributor to differences. Our results provide a number of biomarkers for FLD in salmon, and very strong evidence that prolonged cold exposure can trigger FLD in this ecologically and economically important species.

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.

A Step Forward in the Characterization of Primary Brown Trout Hepatocytic Spheroids as Experimental Models

Mammal hepatocyte spheroids have been investigated as alternative experimental models in several contexts, since three-dimensional (3D) systems have shown the potential to mimic in vivo scenarios. The description of fish hepatocyte 3D models is still minimal. This study intends to further characterize brown trout primary hepatocyte spheroids at distinct time points up to 25 days in culture. Viability, biometry, histomorphology, and basal expression of a selection of genes (metabolism and detoxification, efflux transport, and estrogenic signalling) were considered. The gene expression of whole liver samples from the same fish donor were evaluated concurrently. After 12 days in culture, the hepatocyte spheroids exhibited biometric and morphological stability. From the 12th to the 20th day in culture, the basal expression levels for most of the selected genes did not vary. The targeted mRNA levels were higher in brown trout liver samples compared to hepatocyte spheroids. Despite that, data supported that this model resembles some in vivo features. As an experimental alternative model, it showed potential to be used in a stable time window that can be exploited for exposure tests to different xenobiotics, namely, estrogenic compounds.

Integrative omics-analysis of lipid metabolism regulation by peroxisome proliferator-activated receptor a and b agonists in male Atlantic cod

Lipid metabolism is essential in maintaining energy homeostasis in multicellular organisms. In vertebrates, the peroxisome proliferator-activated receptors (PPARs, NR1C) regulate the expression of many genes involved in these processes. Atlantic cod (Gadus morhua) is an important fish species in the North Atlantic ecosystem and in human nutrition, with a highly fatty liver. Here we study the involvement of Atlantic cod Ppar a and b subtypes in systemic regulation of lipid metabolism using two model agonists after in vivo exposure. WY-14,643, a specific PPARA ligand in mammals, activated cod Ppara1 and Ppara2 in vitro. In vivo, WY-14,643 caused a shift in lipid transport both at transcriptional and translational level in cod. However, WY-14,643 induced fewer genes in the fatty acid beta-oxidation pathway compared to that observed in rodents. Although GW501516 serves as a specific PPARB/D ligand in mammals, this compound activated cod Ppara1 and Ppara2 as well as Pparb in vitro. In vivo, it further induced transcription of Ppar target genes and caused changes in lipid composition of liver and plasma. The integrative approach provide a foundation for understanding how Ppars are engaged in regulating lipid metabolism in Atlantic cod physiology. We have shown that WY-14,643 and GW501516 activate Atlantic cod Ppara and Pparb, affect genes in lipid metabolism pathways, and induce changes in the lipid composition in plasma and liver microsomal membranes. Particularly, the combined transcriptomic, proteomics and lipidomics analyses revealed that effects of WY-14,643 on lipid metabolism are similar to what is known in mammalian studies, suggesting conservation of Ppara functions in mediating lipid metabolic processes in fish. The alterations in the lipid profiles observed after Ppar agonist exposure suggest that other chemicals with similar Ppar receptor affinities may cause disturbances in the lipid regulation of fish. Model organism: Atlantic cod (Gadus morhua). LSID: urn:lsid:zoobank.org:act:389BE401-2718-4CF2-BBAE-2E13A97A5E7B. COL Identifier: 6K72F.

Establishing brown trout primary hepatocyte spheroids as a new alternative experimental model-Testing the effects of 5α-dihydrotestosterone on lipid pathways

Three-dimensional (3D) fish liver cultures mimic the in vivo cellular microenvironment, which is ideal for ecotoxicological research. Despite that, the application of these cultures to evaluate toxic effects in fish is scarce. A 3D model of brown trout (Salmo trutta f. fario) primary hepatocyte spheroids was optimized in this study by using DMEM/F-12 with 15 mM of HEPES, 10 mL/L of an antibiotic and antimycotic solution and FBS 10% (v/v), at 18 °C with ∼100 rpm. The selection of optimal conditions was based on a multiparametric characterization of the spheroids, including biometry, viability, microanatomy and immunohistochemistry. Biometric and morphologic stabilization of spheroids was reached within 12-16 days of culture. To our knowledge, this study is the first to culture and characterize viable spheroids from brown trout primary hepatocytes for over 30 days. Further, the 3D model was tested to explore the androgenic influences on lipidic target genes after 96 h exposures to control, solvent control, 10 and 100 µM of 5α-dihydrotestosterone (DHT), a non-aromatizable androgen. Spheroids exposed to 100 µM of DHT had decreased sphericity. DHT at 100 µM also significantly down-regulated Acox1-3I, PPARγ and fatty acid synthesis targets (i.e., ACC), and significantly up-regulated Fabp1. Acsl1 was significantly up-regulated after exposure to both 10 and 100 µM of DHT. The results support that DHT modulates distinct lipidic pathways in brown trout and show that this 3D model is a new valuable tool for physiological and toxicological mechanistic studies.

Deciphering influences of testosterone and dihydrotestosterone on lipid metabolism genes using brown trout primary hepatocytes

Despite of physiological and toxicological relevance, the potential of androgens to influence fish lipid metabolism remains poorly explored. Here, brown trout primary hepatocytes were exposed to six concentrations (1 nM to 100 μM) of dihydrotestosterone (DHT) and testosterone (T), to assess changes in the mRNA levels of genes covering diverse lipid metabolic pathways. Acsl1, essential for fatty acid activation, was up-regulated by T and DHT, whereas the lipogenic enzymes FAS and ACC were up-regulated by the highest (100 μM) concentration of T and DHT, respectively. ApoA1, the major component of high-density lipoprotein (HDL), was down-regulated by both androgens. PPARγ, linked to adipogenesis and peroxisomal β-oxidation, was down-regulated by T and DHT, while Acox1-3I, rate-limiting in peroxisomal β-oxidation, was down-regulated by T. Fabp1, StAR and LPL were not altered. Our findings suggest that androgens may impact on lipid transport, adipogenesis and fatty acid β-oxidation and promote lipogenesis in fish liver.

Silencing of PPARαBb mRNA in brown trout primary hepatocytes: effects on molecular and morphological targets under the influence of an estrogen and a PPARα agonist

The crosstalk between peroxisome proliferator-activated receptor α (PPARα) and estrogenic pathways are shared from fish to humans. Salmonid fish had an additional genome duplication, and two PPARα isoforms (PPARαBa and PPARαBb) were previously identified. Since a negative regulation between estrogen signaling and PPARα was described, a post-transcriptional gene silencing for PPARαBb was designed in primary brown trout hepatocytes. The aims of the study were to: (i) decipher the effects of PPARαBb knock-down on peroxisome morphology and on mRNA expression of potential target genes, and (ii) to assess the cross-interferences caused by an estrogenic compound (17α-ethinylestradiol - EE2) and a PPARα agonist (Wy-14,643 - Wy) using the established knock-down model. A knock-down efficiency of 70% was achieved for PPARαBb and its silencing significantly reduced the volume density of peroxisomes, but did not alter mRNA levels of the studied genes. Exposure to Wy did not change peroxisome morphology or mRNA expression, but under silencing conditions Wy rescued the volume density of peroxisomes to control levels, and increased acyl-coenzyme A oxidase 1-3l (Acox1-3l) mRNA. Exposure to EE2 caused a reduction of peroxisome volume density, but under silencing conditions this effect was abolished and ApoA1 mRNA level was diminished. The morphological alterations of peroxisomes by WY and EE2 demonstrated that obtained results are PPARαBb dependent, and suggest the regulation of unknown downstream targets of PPARαBb. In summary, PPARαBb is involved in the control of peroxisome size and/or number, which opens future opportunities to explore its regulation and molecular targets.

Sex-steroids and hypolipidemic chemicals impacts on brown trout lipid and peroxisome signaling - Molecular, biochemical and morphological insights

Lipid metabolism involves complex pathways, which are regulated in a similar way across vertebrates. Hormonal and hypolipidemic deregulations cause lipid imbalance from fish to humans, but the underlying mechanisms are far from understood. This study explores the potential of using juvenile brown trout to evaluate the in vivo interferences caused by estrogenic (17α-ethinylestradiol - EE2), androgenic (testosterone - T), and hypolipidemic (clofibrate - CLF) compounds in lipidic and/or peroxisomal pathways. Studied endpoints were from blood/plasma biochemistry, plasma fatty acid profile, ultrastructure of hepatocytes and abundance of their peroxisomes to mRNA expression in the liver. Both T and CLF caused minimal effects when compared to EE2. Estrogenized fish had significantly higher hepatosomatic indexes, increased triglycerides and very-low density lipoproteins (VLDL) in plasma, compared with solvent control. Morphologically, EE2 fish showed increased lipid droplets in hepatocytes, and EE2 and T reduced volume density of peroxisomes in relation to the hepatic parenchyma. Polyunsaturated fatty acids (PUFA) in plasma, namely n-3 PUFA, increased with EE2. EE2 animals had increased mRNA levels of vitellogenin A (VtgA), estrogen receptor alpha (ERα), peroxisome proliferator-activated receptor alpha (PPARα), PPARαBa and acyl-CoA long chain synthetase 1 (Acsl1), while ERβ-1, acyl-CoA oxidase 1-3I (Acox1-3I), Acox3, PPARγ, catalase (Cat), urate oxidase (Uox), fatty acid binding protein 1 (Fabp1) and apolipoprotein AI (ApoAI) were down-regulated. In summary, in vivo EE2 exposure altered lipid metabolism and peroxisome dynamics in brown trout, namely by changing the mRNA levels of several genes. Our model can be used to study possible organism-level impacts, viz. in gonadogenesis.