IL-16 Induces Intestinal Inflammation via PepT1 Upregulation in a Pufferfish Model: New Insights into the Molecular Mechanism of Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) has long been a worldwide health care problem with a persistently increasing incidence. Although its clinical features have been well described, its etiology and pathogenesis remain unclear. IL-16 is a chemoattractant cytokine with various effects on cellular activities and diseases. However, the involvement of IL-16 in IBD remains poorly understood. In this study, to our knowledge we report for the first time the mechanism by which IL-16 induces intestinal inflammation by upregulating the expression of oligopeptide transporter member 1 (PepT1) in a Tetraodon nigroviridis fish model. The dextran sodium sulfate-induced colitis model in this species revealed that IL-16 levels significantly increase accompanied by elevations in PepT1 in the colon. Moreover, the signs of colitis were dramatically attenuated by IL-16 depletion using anti-IL-16 Abs. In vivo IL-16 administration induced remarkable intestinal inflammation with typical ulcerative colitis-like features, including histologic damage, inflammatory cell infiltration, increased myeloperoxidase activity, and proinflammatory cytokines expression, which corresponded with significant PepT1 upregulation in the colon. The IL-16-induced PepT1 expression and its upregulated fMLF transport were also demonstrated in vitro. To our knowledge, our study provides the first evidence of the connection between IL-16 and PepT1, which provides new insights into the molecular mechanism underlying IBD development. Additionally, this study suggests that fish species are an attractive model for studying IBD. By providing a better understanding of IL-16 biology from fish to mammals, this study should aid the development of IL-16-based therapies for IBD.