AUTHOR=Wang Jie , Lei Peng , Gamil Amr Ahmed Abdelrahim , Lagos Leidy , Yue Yang , Schirmer Kristin , Mydland Liv Torunn , Øverland Margareth , Krogdahl Åshild , Kortner Trond M. 

TITLE=Rainbow Trout (Oncorhynchus Mykiss) Intestinal Epithelial Cells as a Model for Studying Gut Immune Function and Effects of Functional Feed Ingredients

JOURNAL=Frontiers in Immunology

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2019.00152

DOI=10.3389/fimmu.2019.00152

ISSN=1664-3224

ABSTRACT=<p>The objective of this study was to evaluate the suitability of the rainbow trout intestinal epithelial cell line (RTgutGC) as an <italic>in vitro</italic> model for studies of gut immune function and effects of functional feed ingredients. Effects of lipopolysaccharide (LPS) and three functional feed ingredients [nucleotides, mannanoligosaccharides (MOS), and beta-glucans] were evaluated in RTgutGC cells grown on conventional culture plates and transwell membranes. Permeation of fluorescently-labeled albumin, transepithelial electrical resistance (TEER), and tight junction protein expression confirmed the barrier function of the cells. Brush border membrane enzyme activities [leucine aminopeptidase (LAP) and maltase] were detected in the RTgutGC cells but activity levels were not modulated by any of the exposures. Immune related genes were expressed at comparable relative basal levels as these in rainbow trout distal intestine. LPS produced markedly elevated gene expression levels of the pro-inflammatory cytokines <italic>il1b, il6, il8</italic>, and <italic>tnfa</italic> but had no effect on ROS production. Immunostaining demonstrated increased F-actin contents after LPS exposure. Among the functional feed ingredients, MOS seemed to be the most potent modulator of RTgutGC immune and barrier function. MOS significantly increased albumin permeation and <italic>il1b, il6, il8, tnfa</italic>, and <italic>tgfb</italic> expression, but suppressed ROS production, cell proliferation and <italic>myd88</italic> expression. Induced levels of <italic>il1b</italic> and <italic>il8</italic> were also observed after treatment with nucleotides and beta-glucans. For barrier function related genes, all treatments up-regulated the expression of <italic>cldn3</italic> and suppressed <italic>cdh1</italic> levels. Beta-glucans increased TEER levels and F-actin content. Collectively, the present study has provided new information on how functional ingredients commonly applied in aquafeeds can affect intestinal epithelial function in fish. Our findings suggest that RTgutGC cells possess characteristic features of functional intestinal epithelial cells indicating a potential for use as an efficient <italic>in vitro</italic> model to evaluate effects of bioactive feed ingredients on gut immune and barrier functions and their underlying cellular mechanisms.</p>