Non-coding keratin variants associate with fibrosis progression in hemochromatosis patients

Background and Aims: Keratins 8 and 18 (K8/K18) protect the liver from various forms of injury. Accordingly, exonic K8/K18 variants associate with adverse outcome of acute liver failure and with liver fibrosis progression in patients with chronic hepatitis C infection or primary biliary cirrhosis. An overexpression of K8/K18 variants in hemochromatosis patients was also reported, but no association with liver fibrosis development was seen. Methods: To study the role of keratin variants in hemochromatosis, we analyzed the entire exonic regions of K8/K18 in 240 European hemochromatosis patients all carrying a homozygous C282Y HFE mutation. Exonic regions were PCR-amplified and analyzed using denaturing high-performance liquid chromatography and DNA sequencing. To study the effect of presence of K8 variants on iron metabolism, mice overexpressing wild-type (WT) K8 or K8 G62C were fed 3% iron carbonyl-containing diet for four weeks. Results: Our findings showed amino acid altering keratin heterozygous variants in 23 of 240 hemochromatosis patients (9.5%) and non-coding heterozygous variants in 20 patients (8.3%). Two novel K8 variants (Q169E/ R275W) were found. K8 R341H was the most common amino-acid altering variant (12 patients) and exclusively associated with an intronic KRT8 IVS7+10delC deletion. Amino-acid-altering variants were significantly more common in Swedish patients compared to Austrians (15 vs. 6.2%, p<0.05). Intronic, but not amino-acid altering variants associated with liver fibrosis development. Interestingly, iron-enriched diet led to lower iron liver deposition in K8 G62C vs. K8 WT animals (6232 vs. 5319, p=0.05), while comparable iron liver contents were observed in both strains under basal conditions. Conclusions: In hemochromatosis patients, intronic K8/K18 variants predispose to liver fibrosis development. Keratin variant frequency displays a high variability among geographic regions.