Keratin 23 represents a novel liver injury marker reflecting the severity of ductular reaction

Abstract

Keratins (K) are the intermediate filaments of epithelial cells and constitute established diagnostic tools. In the liver, K7/K19 expression is restricted to hepatic progenitor cells (HPCs) and biliary epithelial cells (BECs). Consequently, K7/K19 represent a widely used marker of the regenerative liver response termed ductular reaction (DR) that consists of activated BECs and HPCs. Methods: Since K23 is a largely unknown keratin family member, we analysed its expression and localization in selected human liver disorders and mouse liver injury models using custom-made antibodies. Serum K23 levels were measured via dot blot analysis. K23 regulation in response to IL1b was studied in hepatocellular and bile duct carcinoma cell lines. Results: In untreated mice, K23 was found in biliary epithelia but not hepatocytes. It was (together with K7/K19) markedly up-regulated in three different DR/cholestatic injury models, i.e. MDR2 knockouts, animals treated with 3,5-diethoxycarbonyl-1,4-dihydrocollidine or subjected to bile duct ligation. No changes in K23 levels were seen in hepatocellular injury models such as partial hepatectomy or carbon tetrachloride-induced fibrogenesis. K23 levels correlated with the DR marker Fn14 and immunofluorescence staining showed a distinct but not perfect co-localization with K7/K19. In cell culture, K23 expression was upregulated after IL1b treatment. In humans, K23 levels were moderately up-regulated in active HCV (˜3 times) and ALD (˜10 times). K23 expression was higher in patients with more prominent inflammation/fibrosis. A dramatic increase (> 200 times) was observed in patients with ALF and end-stage PBC. K23 serum levels were significantly higher in patients with alcoholic liver cirrhosis compared to control subjects. In conclusion, K23 represents a novel, stress inducible DR marker and its levels correlate with the severity of the liver disease. Given its release into the serum and its rather specific expression pattern, it may represent an attractive non-invasive marker of liver injury/regeneration.