Colorectal hyperplasia and inflammation in keratin 8-deficient FVB/N mice.

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Abstract
We report that keratin 8 (mK8) gene disruption causes colorectal hyperplasia in FVB/N mice. The intestinal lesions affect uniformly the cecum, colon, and rectum but not the small intestine. The elongation of the crypts is accompanied by an inflammation of the lamina propria and submucosa. Hepatic, renal, and pancreatic functions tested in clinical assays are within nonpathological range, suggesting that the major defect lies in colonic epithelial cells. Still, small but consistent elevation in the hepatic enzymes alanine (AST) and asparate (ALT) aminotransferase are observed, along with a 70% increase in spleen weight. No homozygous mouse line has been established, because of a markedly reduced fertility of the mK8-/- females. Previously, we reported that the mK8- targeted mutation causes embryonic lethality in (C57B1/6x129Sv) mice. This strong effect of the genetic background on the mK8- mutant phenotype emphasizes the importance of using several inbred mouse strains to reveal the polygenic contribution to mutant phenotypes. Our results demonstrate that genetic modifiers of K8/K18 filament functions, with profound effects on embryogenesis and gut functional integrity, are differentially active in the FVB/N and C57B1/6 genetic backgrounds. More importantly, the increase in mK8-/- gut epithelial cell number, rather than cell disruption, contrasts with the known function of epidermal keratins in providing mechanical strength.