OCLN and colitis: 128 Activation of AhR by the microbial metabolite Urolithin A (UroA) mitigated symptoms of DSS-induced colitis in mice, but this effect was absent in Cyp1a1-/- animals.129 Furthermore, wildtype mice treated with UroA showed reduced FITC-dextran staining and significant increases in ZO-1, occludin, and claudin-4, whereas Cyp1a1-/- mice did not exhibit improvement.129 This suggests that while AhR activation by certain immune pathways can protect barrier integrity, prolonged activation (as seen in MRSA infection) may impair the intestinal epithelium barrier.130