Osteopontin Protects Colonic Mucosa from Dextran Sodium Sulfate-Induced Acute Colitis in Mice by Regulating Junctional Distribution of Occludin
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Osteopontin (OPN) has been reported to play an important role in intestinal mucosal protection. Although OPN may have positive effects on tight junctions, the exact relationship between OPN and tight junctions has yet to be elucidated.
To investigate the role of OPN on tight junctions.
We evaluated clinical signs and histopathology of acute colitis induced by dextran sodium sulfate (DSS) in OPN knockout and wild-type (WT) mice in vivo. Expression levels of occludin and zonula occludens-1 were examined using immunofluorescence. For in vitro analysis, an siRNA-mediated OPN-suppressed Caco-2 monolayer was used. Expression levels and patterns of occludin were analyzed by immunofluorescence, and transepithelial electrical resistance (TER) was measured to evaluate barrier function. Triton X-100 fractionation was used to analyze phosphorylated occludin associated with tight junctional localization.
OPN deficiency resulted in an elevated disease activity index, shortened colon length, and aggravated histological signs in mice with DSS-induced acute colitis compared to WT mice. OPN deficiency decreased occludin expression in the colonic mucosa. In Caco-2 monolayers, OPN suppression reduced junctional occludin and redistributed it into the intracellular compartment with decreased TER. Furthermore, western blot for occludin from Triton X-100 insoluble fraction revealed that OPN suppression reduced the phosphorylated form of occludin, which is actually distributed in the tight junction.
Our study showed that OPN is essential for maintaining the tight junction complex by allowing occludin to localize at tight junctions. This could constitute additional evidence that OPN plays a crucial role in intestinal mucosal protection.
KeywordsMucosal protection Osteopontin Occludin Tight junction
This study was supported by the Research Institute of Veterinary Science, College of Veterinary Medicine, Seoul National University and by the Korea Mouse Phenotyping Project (NRF-2016M3A9D5A01952416) of a National Research Foundation grant funded by the Korean government (MSIP).
Compliance with ethical standards
Conflict of interest
All authors declare that they have no conflict of interest.
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