The role of inherited keratin variants in liver disease development

Abstract

Keratins 8 and 18 (K8/K18) are the major intermediate filaments of simple epithelia and the only keratins expressed in adult hepatocytes. K8/K18 variants associate with liver fibrosis progression in patients with chronic hepatitis C (CHC) and primary biliary cirrhosis. To better define the importance of K8/K18 variants in hereditary hemochromatosis (HHC) and chronic hepatitis C infection (CHC), we analysed a cohort of 162 European hemochromatosis patients and an US cohort of 1222 patients. Genomic DNA was isolated from peripheral blood. PCR-amplified exonic regions carrying K8/K18 mutational hot-spots analyzed using denaturing high-performance liquid chromatography and DNA sequencing. The biological significance of novel K8/K18 variants was assessed in transfected cell lines. Transgenic animals overexpressing K8 G62C variant were subjected to the established liver fibrosis models and a nutritional iron overload. Finally the iron toxicity was analysed in the primary hepatocytes isolated from K8 G62C animals. Among CHC patients, African American patients had the highest frequency of amino acid altering K8/K18 variants (p<0.05); Among Caucasians, K8 R341H/G62C were the most common ones, whereas K8 A333A/G434S were most numerous in African-Americans. K8 variants are significantly overrepresented in cirrhotic patients with CHC (p=0.03). K8/K18 variants associated with adverse CHC outcome. The novel K18 R45P variant increased keratin solubility in vitro. Among the HHC patients, the non-coding KRT8 variants were significantly overrepresented in cirrhotic patients (p=0.02). In transgenic mice and primary hepatocytes, the presence of K8 G62C variant did not affect the extent of iron-accumulation or the magnitude of iron-induced hepatocellular injury. K8 G62C variants did not predispose to liver fibrosis development in three different established liver fibrosis models. Consequently, exonic K8/K18 variants predispose to CHC disease progression and some variants segregate with unique ethnic/race backgrounds. Intronic K8/18 variants associate with liver fibrosis progression in patients with HHC, but not with CHC. The experimental data do not support the importance of K8 G62C variant in development of iron-mediated liver injury or liver fibrosis development in general.