Polarized Trout Epithelial Cells Regulate Transepithelial Electrical Resistance, Gene Expression, and the Phosphoproteome in Response to Viral Infection

New Insights in Microplastic Cellular Uptake Through a Cell-Based Organotypic Rainbow-Trout (Oncorhynchus mykiss) Intestinal Platform

Microplastics (MPs) in fish can cross the intestinal barrier and are often bioaccumulated in several tissues, causing adverse effects. While the impacts of MPs on fish are well documented, the mechanisms of their cellular internalization remain unclear. A rainbow-trout (Oncorhynchus mykiss) intestinal platform, comprising proximal and distal intestinal epithelial cells cultured on an Alvetex scaffold, was exposed to 50 mg/L of MPs (size 1-5 µm) for 2, 4, and 6 h. MP uptake was faster in RTpi-MI compared to RTdi-MI. Exposure to microplastics compromised the cellular barrier integrity by disrupting the tight-junction protein zonula occludens-1, inducing significant decreases in the transepithelial-electrical-resistance (TEER) values. Consequently, MPs were internalized by cultured epithelial cells and fibroblasts. The expression of genes related to endocytosis (cltca, cav1), macropinocytosis (rac1), and tight junctions' formation (oclna, cldn3a, ZO-1) was analyzed. No significant differences were observed in cltca, oclna, and cldn3a expression, while an upregulation of cav1, rac1, and ZO-1 genes was detected, suggesting macropinocytosis as the route of internalization, since also cav1 and ZO-1 are indirectly related to this mechanism. The obtained results are consistent with data previously reported in vivo, confirming its validity for identifying MP internalization pathways. This could help to develop strategies to mitigate MP absorption through ingestion.

Single and combined effects of titanium (TiO2) and zinc (ZnO) oxide nanoparticles in the rainbow trout gill cell line RTgill-W1

Understanding the environmental impact of nanoparticle (NP) mixtures is essential to accurately assess the risk they represent for aquatic ecosystems. However, although the toxicity of individual NPs has been extensively studied, information regarding the toxicity of combined NPs is still comparatively rather scarce. Hence, this research aimed to investigate the individual and combined toxicity mechanisms of two widely consumed nanoparticles, zinc oxide (ZnO NPs) and titanium dioxide (TiO2 NPs), using an in vitro model, the RTgill-W1 rainbow trout gill epithelial cell line. Sublethal concentrations of ZnO NPs (0.1 µg mL-1) and TiO2 (30 µg mL-1) and a lethal concentration of ZnO NPs causing 10% mortality (EC10, 3 µg mL-1) were selected based on cytotoxicity assays. Cells were then exposed to the NPs at the selected concentrations alone and to their combination. Cytotoxicity assays, oxidative stress markers, and targeted gene expression analyses were employed to assess the NP cellular toxicity mechanisms and their effects on the gill cells. The cytotoxicity of the mixture was identical to the one of ZnO NPs alone. Enzymatic and gene expression (nrf2, gpx, sod) analyses suggest that none of the tested conditions induced a strong redox imbalance. Metal detoxification mechanisms (mtb) and zinc transportation (znt1) were affected only in cells exposed to ZnO NPs, while tight junction proteins (zo1 and cldn1), and apoptosis protein p53 were overexpressed only in cells exposed to the mixture. Osmoregulation (Na + /K + ATPase gene expression) was not affected by the tested conditions. The overall results suggest that the toxic effects of ZnO and TiO2 NPs in the mixture were significantly enhanced and could result in the disruption of the gill epithelium integrity. This study provides new insights into the combined effects of commonly used nanoparticles, emphasizing the importance of further investigating how their toxicity may be influenced in mixtures.

Isolation and characterisation of two epithelial-like cell lines from the gills of Chrysophrys auratus (Australasian snapper) and Oncorhynchus tshawytscha (Chinook salmon) and their use in aquatic toxicology

In vitro gill models are becoming increasingly important in aquatic toxicology, yet the fish gill invitrome is underrepresented, encompassing approximately 0.1% of extant species. Here, we describe the establishment and characterisation of two gill-derived, epithelial-like cell lines isolated from fish species of significant importance to New Zealand: Chrysophrys auratus (Australasian snapper) and Oncorhynchus tshawytscha (Chinook salmon). Designated CAgill1PFR (Chrysophrys auratus, gill 1, Plant & Food Research) and OTgill1PFR (Oncorhynchus tshawytscha, gill 1, Plant & Food Research), these cell lines have each been passaged greater than each 70 times over several years and are considered spontaneously immortalised. Both cell lines required serum for growth and exhibited differential responses to basal media formulations. CAgill1PFR was sensitive to low temperatures (4 °C) but replicated at high temperatures (30 °C), whereas OTgill1PFR was sensitive to high temperatures but remained viable at low temperatures, mirroring the natural environment of their host species. Immunostaining revealed expression of epithelial cell markers cytokeratin and E-cadherin, alongside positivity for the mesenchymal cell marker, vimentin. CAgill1PFR was more sensitive to the environmental toxin 3,4 dichloroaniline than OTgill1PFR through measurements of metabolic activity, membrane integrity, and lysosomal function. Furthermore, CAgill1PFR produced less CYP1A activity, indicative of ongoing biotransformation processes, in response to beta-naphthoflavone than OTgill1PFR. These cell lines expand the toolbox of resources and emphasise the need for species-specific aquatic toxicology research.

Helicobacter pylori and Epstein-Barr virus infection in cell polarity alterations

The asymmetrical distribution of the cellular organelles inside the cell is maintained by a group of cell polarity proteins. The maintenance of polarity is one of the vital host defense mechanisms against pathogens, and the loss of it contributes to infection facilitation and cancer progression. Studies have suggested that infection of viruses and bacteria alters cell polarity. Helicobacter pylori and Epstein-Barr virus are group I carcinogens involved in the progression of multiple clinical conditions besides gastric cancer (GC) and Burkitt's lymphoma, respectively. Moreover, the coinfection of both these pathogens contributes to a highly aggressive form of GC. H. pylori and EBV target the host cell polarity complexes for their pathogenesis. H. pylori-associated proteins like CagA, VacA OipA, and urease were shown to imbalance the cellular homeostasis by altering the cell polarity. Similarly, EBV-associated genes LMP1, LMP2A, LMP2B, EBNA3C, and EBNA1 also contribute to altered cell asymmetry. This review summarized all the possible mechanisms involved in cell polarity deformation in H. pylori and EBV-infected epithelial cells. We have also discussed deregulated molecular pathways like NF-κB, TGF-β/SMAD, and β-catenin in H. pylori, EBV, and their coinfection that further modulate PAR, SCRIB, or CRB polarity complexes in epithelial cells.

Influenza H7N9 virus disrupts the monolayer human brain microvascular endothelial cells barrier in vitro

Influenza H7N9 virus causes human infections with about 40% case fatality rate. The severe cases usually present with pneumonia; however, some present with central nervous system complications. Pneumonia syndrome is attributed to the cytokine storm after infection with H7N9, but the pathogenic mechanism of central nervous system complications has not been clarified. This study used immortalized human brain microvascular endothelial cells hCMEC/D3 to simulate the blood-brain barrier. It demonstrated that H7N9 virus could infect brain microvascular endothelial cells and compromise the blood-brain barrier integrity and permeability by down-regulating the expression of cell junction-related proteins, including claudin-5, occludin, and vascular endothelial (VE)-cadherin. These results suggested that H7N9 could infect the blood-brain barrier in vitro and affect its functions, which could be a potential mechanism for the pathogenesis of H7N9 viral encephalopathy.

Establishment of an In Vitro Model to Study Viral Infections of the Fish Intestinal Epithelium

Viral infections are still a major concern for the aquaculture industry. For salmonid fish, even though breeding strategies and vaccine development have reduced disease outbreaks, viral diseases remain among the main challenges having a negative impact on the welfare of fish and causing massive economic losses for the industry. The main entry port for viruses into the fish is through mucosal surfaces including that of the gastrointestinal tract. The contradictory functions of this surface, both creating a barrier towards the external environment and at the same time being responsible for the uptake of nutrients and ion/water regulation make it particularly vulnerable. The connection between dietary components and viral infections in fish has been poorly investigated and until now, a fish intestinal in vitro model to investigate virus-host interactions has been lacking. Here, we established the permissiveness of the rainbow trout intestinal cell line RTgutGC towards the important salmonid viruses-infectious pancreatic necrosis virus (IPNV), salmonid alphavirus (subtype 3, SAV3) and infectious salmon anemia virus (ISAV)-and explored the infection mechanisms of the three different viruses in these cells at different virus to cell ratios. Cytopathic effect (CPE), virus replication in the RTgutGC cells, antiviral cell responses and viral effects on the barrier permeability of polarized cells were investigated. We found that all virus species infected and replicated in RTgutGC cells, although with different replication kinetics and ability to induce CPE and host responses. The onset and progression of CPE was more rapid at high multiplicity of infection (MOI) for IPNV and SAV3 while the opposite was true of ISAV. A positive correlation between the MOI used and the induction of antiviral responses was observed for IPNV while a negative correlation was detected for SAV3. Viral infections compromised barrier integrity at early time points prior to observations of CPE microscopically. Further, the replication of IPNV and ISAV had a more pronounced effect on barrier function than SAV3. The in vitro infection model established herein can thus provide a novel tool to generate knowledge about the infection pathways and mechanisms used to surpass the intestinal epithelium in salmonid fish, and to study how a virus can potentially compromise gut epithelial barrier functions.

Differential response of RTGUTGC and RTGILL-W1 rainbow trout epithelial cell lines to viral stimulation

Mucosal surfaces constitute the main route of entry of pathogens into the host. In fish, these mucosal tissues include, among others, the gastrointestinal tract, the gills and the skin. However, knowledge about the mechanisms of regulation of immunity in these tissues is still scarce, being essential to generate a solid base that allows the development of prevention strategies against these infectious agents. In this work, we have used the RTgutGC and RTgill-W1 epithelial-like cell lines, derived from the gastrointestinal tract and the gill of rainbow trout (Oncorhynchus mykiss), respectively, to investigate the transcriptional response of mucosal epithelial cells to a viral mimic, the dsRNA poly I:C, as well as to two important viral rainbow trout pathogens, namely viral haemorrhagic septicaemia virus (VHSV) and infectious pancreatic necrosis virus (IPNV). Additionally, we have established how the exposure to poly I:C affected the susceptibility of RTgutGC and RTgill-W1 cells to both viruses. Our results reveal important differences in the way these two cell lines respond to viral stimuli, providing interesting information on these cell lines that have emerged in the past years as useful tools to study mucosal responses in fish.

Dopamine D1 receptor agonist alleviates acute lung injury via modulating inflammatory responses in macrophages and barrier function in airway epithelial cells

Acute lung injury (ALI) or its severe form, acute respiratory distress syndrome (ARDS) is a life-threatening illness without effective therapeutic interventions currently. Multiple lines of evidence indicated that overwhelming inflammatory responses and impaired epithelial barrier contributed to the pathogenesis of ALI/ARDS. Recently, dopamine (DA) system was identified to participate in various pulmonary diseases. Here, we discovered that dopamine D1-like receptors mainly expressed in macrophages and airway epithelial cells (AECs), which were downregulated by lipopolysaccharide (LPS) challenge in ALI mouse lung. SKF38393 (SKF) is a selective agonist for D1-like receptors and was demonstrated to inhibit excessive inflammatory responses and oxidative stress in THP-1 cell-derived macrophages and Beas-2B cells, as well as improve airway epithelial barrier dysfunction induced by LPS stimulation. Moreover, SKF administration could effectively decrease pulmonary inflammation, ameliorate tissue damage in the LPS-triggered ALI mice. The broad protective actions of SKF might be attributed to the activation of Nrf2 antioxidative system by use of the specific inhibitor, ML385. This study offers evidence of potent immunoregulatory activity of SKF in macrophages, AECs as well as ALI mouse model, which opens novel therapeutic avenues for the intervention of ALI/ARDS.

Evaluation of establishment and maintenance of primary cell cultures from several strains of common carp (Cyprinus carpio L.)

As a surrogate for the whole organism, primary cultures and cell lines serve as valuable tools for investigating exogenous and endogenous cytopathy. Studying cell responsiveness to diseases and contaminants is considered a less demanding and more readily accessible research approach that minimizes animal distress and provides more specific data. In the current work, the authors established primary cultures from several different organs and tissues of common carp (Cyprinus carpio L.) for subsequent use in other applications. They investigated the technical challenges in obtaining successful and durable carp-derived tissue cultures. The trials indicate that the type of tissue grown, carp strain and fish age impact equally upon culturing success, as do the cultivating conditions. Cells from gill epithelia, head and trunk kidneys, spleen, skin, gonads and ocular tissue were successfully established and maintained for further use in in-vitro testing. The primary cultures were, therefore, used to investigate and assess pathogens and pollutants emerging in carp's environment.

Human Norovirus Induces Aquaporin 1 Production by Activating NF-κB Signaling Pathway

Human norovirus (HuNoV) is one of the major pathogens of acute nonbacterial gastroenteritis. Due to the lack of a robust and reproducible in vitro culture system and an appropriate animal model, the mechanism underlying HuNoV-caused diarrhea remains unknown. In the current study, we found that HuNoV transfection induced the expression of aquaporin 1 (AQP1), which was further confirmed in the context of virus infection, whereas the enterovirus EV71 (enterovirus 71) did not have such an effect. We further revealed that VP1, the major capsid protein of HuNoV, was crucial in promoting AQP1 expression. Mechanistically, HuNoV induces AQP1 production through the NF-κB signaling pathway via inducing the expression, phosphorylation and nuclear translocation of p65. By using a model of human intestinal epithelial barrier (IEB), we demonstrated that HuNoV and VP1-mediated enhancement of small molecule permeability is associated with the AQP1 channel. Collectively, we revealed that HuNoV induced the production of AQP1 by activating the NF-κB signaling pathway. The findings in this study provide a basis for further understanding the significance of HuNoV-induced AQP1 expression and the potential mechanism underlying HuNoV-caused diarrhea.