The Amount of Keratins Matters for Stress Protection of the Colonic Epithelium

<div><p>Keratins (K) are important for epithelial stress protection as evidenced by keratin mutations predisposing to human liver diseases and possibly inflammatory bowel diseases. A role for K8 in the colon is supported by the ulcerative colitis-phenotype with epithelial hyperproliferation and abnormal ion transport in K8-knockout (K8^−/−) mice. The heterozygote knockout (K8^+/−) colon appears normal but displays a partial ion transport-defect. Characterizing the colonic phenotype we show that K8^+/− colon expresses ~50% less keratins compared to K8 wild type (K8^+/+) but <i>de novo</i> K7 expression is observed in the top-most cells of the K8^+/− and K8^−/− crypts. The K8^+/− colonic crypts are significantly longer due to increased epithelial hyperproliferation, but display no defects in apoptosis or inflammation in contrast to K8^−/−. When exposed to colitis using the dextran sulphate sodium-model, K8^+/− mice showed higher disease sensitivity and delayed recovery compared to K8^+/+ littermates. Therefore, the K8^+/− mild colonic phenotype correlates with decreased keratin levels and increased sensitivity to experimental colitis, suggesting that a sufficient amount of keratin is needed for efficient stress protection in the colonic epithelia.</p>