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Inflammation of gill epithelia in fish causes increased permeation of polar organic chemicals from OSPW via disruption of tight junctions

ABSTRACT: The epithelial cell layer that lines the fish gill controls the paracellular permeation of chemicals through tight junctions. The integrity of tight junctions can be affected by inflammation, which is likely to impact the branchial bioavailability of chemicals. In this study, we experimentally induced inflammation in the rainbow trout gill cell line RTgill-W1 via exposure to bacterial lipopolysaccharides (LPS). We then co-exposed the cells to extracts of oil sands process-affected water (OSPW), which contain a complex mixture of toxicologically relevant chemicals. Cells exposed to LPS showed a significant reduction in transepithelial electrical resistance (TEER), an indicator of tight junction integrity, after 24 h of exposure. Quantitative RT-PCR analysis determined that the abundance of transcripts of genes coding for tight junction proteins (Claudin 28b and 10e) was significantly decreased in cells exposed to 20, 50, and 100 mg L-1 LPS. Chemical analysis revealed a significant increase in permeation of constituents of OSPW across the gill cell epithelial layer at all studied LPS concentrations. These in vitro findings were confirmed in vivo in rainbow trout fingerlings exposed to both LPS and 10% OSPW for 48 h, which similarly resulted in an increase in chemical uptake relative to fish exposed to OSPW alone. This research demonstrated that inflammation of gill epithelia and the resulting disruption of tight junction integrity could lead to significantly greater uptake of potentially harmful chemicals from the environment, which has important implications for risk assessment.

ORGANISM(S): Oncorhynchus mykiss

PROVIDER: GSE182953 | GEO | 2022/02/28

REPOSITORIES: GEO

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Project description:Background: Rainbow trout (Oncorhynchus mykiss) is a salmonid species with a complex life-history. Wild populations are naturally divided into freshwater residents and sea-run migrants. Migrants undergo an energy-demanding adaptation for life in seawater, known as smoltification, while freshwater residents display these changes in an attenuated magnitude and rate. Despite this, in seawater rainbow trout farming all animals are transferred to seawater. Under these circumstances, weeks after seawater transfer, a significant portion of the fish die (around 10%) or experience growth stunting (GS; around 10%), which represents an important profitability and welfare issue. The underlying causes leading to GS in seawater-transferred rainbow trout remain unknown. In this study, we aimed at characterising the GS phenotype in seawater-transferred rainbow trout using untargeted and targeted approaches. To this end, the liver proteome (LC-MS/MS) and lipidome (LC-MS) of GS and fast-growing phenotypes were profiled to identify molecules and processes that are characteristic of the GS phenotype. Moreover, the transcription, abundance or activity of key proteins and hormones related to osmoregulation (Gill Na+, K+–ATPase activity), growth (plasma IGF-I, and liver igf1, igfbp1b, ghr1 and ctsl) and stress (plasma cortisol) were measured using targeted approaches. Results: No differences in Gill Na+, K+–ATPase activity and plasma cortisol were detected between the two groups. However, a significant downregulation in plasma IGF-I and liver igf1 transcription pointed at this growth factor as an important pathomechanism for GS. Changes in the liver proteome revealed reactive-oxygen-species-mediated endoplasmic reticulum stress as a key mechanism underlying the GS phenotype. From the lipidomic analysis, key observations include a reduction in triacylglycerols and elevated amounts of cardiolipins, a characteristic lipid class associated with oxidative stress, in GS phenotype. Conclusion: While the triggers to the activation of endoplasmic reticulum stress are still unknown, data from this study point towards either an unresolved infection or a nutritional deficiency as underlying drivers of this phenotype.

Project description:Whirling disease, caused by the pathogen Myxobolus cerebralis, afflicts several salmonid species. Rainbow trout are particularly susceptible and suffer high mortality rates. The disease is persistent and spreading in hatcheries and natural waters of several countries, including the U.S., and the economic losses associated with whirling disease have been extremely large. In this study, gene expression profiling was conducted for resistant and susceptible rainbow trout strains following pathogen exposure with the primary objective of identifying specific genes associated with whirling disease resistance. Several genes were significantly up-regulated in skin following pathogen exposure for both the resistant Hofer and susceptible Trout Lodge rainbow trout strains. For both strains, response to infection appears to be associated with the interferon system. Metallothionein is differentially expressed between the resistant and susceptible strains and is a good candidate for future studies due to its diverse functional roles in inflammation and immune response. The present study has provided the first examination into the genetic basis underlying rainbow trout’s immune response and resistance to the whirling disease pathogen. The identified genes have allowed us to gain initial insight into the molecular mechanisms associated with a salmonid host’s immune response and resistance to whirling disease infection. Keywords: Disease state comparison. 1st comparison: exposed vs control. 2nd comparison: resistant vs susceptible strains Resistant (Hofer) and susceptible (Trout Lodge) rainbow trout strains were exposed to 2,000 triactinomyxons (whirling disease pathogen) per fish. Unexposed controls for each strain were treated identically to exposed other than their lack of pathogen exposure. After twenty-four hours, caudal fin tissue was collected for RNA extraction. Amplified RNA was competitively hybridized (exposed versus control) for each strain. Four biological replicates were used for each experimental condition and a balanced block design was incorporated.

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Inflammation of gill epithelia in fish causes increased permeation of polar organic chemicals from OSPW via disruption of tight junctions

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