In vitro fish mucosal surfaces producing mucin as a model for studying host-pathogen interactions.

Current prophylactic and disease control measures in aquaculture highlight the need of alternative strategies to prevent disease and reduce antibiotic use. Mucus covered mucosal surfaces are the first barriers pathogens encounter. Mucus, which is mainly composed of highly glycosylated mucins, has the potential to contribute to disease prevention if we can strengthen this barrier. Therefore, aim of this study was to develop and characterize fish in vitro mucosal surface models based on commercially available cell lines that are functionally relevant for studies on mucin regulation and host-pathogen interactions. The rainbow trout (Oncorhynchus mykiss) gill epithelial cell line RTgill-W1 and the embryonic cell line from Chinook salmon (Oncorhynchus tshawytscha) CHSE-214 were grown on polycarbonate membrane inserts and chemically treated to differentiate the cells into mucus producing cells. RTGill-W1 and CHSE-214 formed an adherent layer at two weeks post-confluence, which further responded to treatment with the γ-secretase inhibitor DAPT and prolonged culture by increasing the mucin production. Mucins were metabolically labelled with N-azidoacetylgalactosamine 6 h post addition to the in vitro membranes. The level of incorporated label was relatively similar between membranes based on RTgill-W1, while larger interindividual variation was observed among the CHSE in vitro membranes. Furthermore, O-glycomics of RTgill-W1 cell lysates identified three sialylated O-glycans, namely Galβ1-3(NeuAcα2-6)GalNAcol, NeuAcα-Galβ1-3GalNAcol and NeuAcα-Galβ1-3(NeuAcα2-6)GalNAcol, resembling the glycosylation present in rainbow trout gill mucin. These glycans were also present in CHSE-214. Additionally, we demonstrated binding of the fish pathogen A. salmonicida to RTgill-W1 and CHSE-214 cell lysates. Thus, these models have similarities to in vivo mucosal surfaces and can be used to investigate the effect of pathogens and modulatory components on mucin production.