Metrnl protects intestinal barrier function by regulating tight junctions via the IKKβ/IκBα/NFκB/MLCK/MLC signaling pathway

Meteorin-like (Metrnl), also known as Subfatin, IL-41, or Cometin, is a secreted protein predominantly expressed in the intestinal epithelium. The intestinal barrier, primarily consisting of epithelial cells connected by tight junctions, is essential for maintaining gut homeostasis by preventing harmful substances from entering the body. Despite Metrnl's high expression in the intestine, its role in barrier function remains unclear. In this study, we investigated Metrnl's role in intestinal barrier function using both loss-of-function (using global and intestinal epithelium-specific knockout mice) and gain-of-function (using intestinal epithelium-specific overexpression mice) approaches. Our findings showed that Metrnl deficiency disrupted tight junctions between enterocytes and exacerbated endotoxin-induced barrier dysfunction. Mechanistically, Metrnl deficiency triggered activation of the IKKβ/IκBα/NFκB signaling pathway, leading to increased MLCK expression and MLC phosphorylation. The NFκB inhibitor PDTC reversed this effect both in vivo and in vitro. Macrophages played an essential role in Metrnl's intestinal barrier protective effects during endotoxemia, but were not necessary in burn-induced barrier injury, suggesting potential differences in mechanism between these conditions. Notably, recombinant Metrnl protein administration protected against barrier dysfunction, and genetic overexpression of Metrnl in enterocytes preserved barrier function and alleviated DSS-induced colitis. These findings establish Metrnl as a key regulator of intestinal barrier integrity through the IKKβ/IκBα/NFκB/MLCK/MLC pathway, highlighting its potential therapeutic value in treating barrier dysfunction disorders. Intestinal barrier dysfunction triggers, such as endotoxin and severe burns, may induce the release of Metrnl from vascular endothelium. This leads to an increase in circulating Metrnl. Both circulating Metrnl and local Metrnl inhibit inflammation and the IKKβ/IκBα/NFκB/MLCK/MLC signaling pathway in enterocytes, thereby protecting tight junctions from disruption caused by endotoxin or burns.