Hepcidin knockout mice develop chronic liver injury and liver fibrosis as a consequence of lysosomal iron overload

Abstract

Background and Aims: Hepcidin is the central regulator of iron homeostasis. Disrupted hepcidin signaling results in hereditary hemochromatosis and iron overload seen in chronic liver disorders. While the association between iron overload and development of end-stage liver disease is well established, the understanding of the underlying mechanisms is hampered by the lack of a suitable animal model. To circumvent this problem, we analyzed hepcidin-knockout (KO) mice as a model of iron-overload associated liver disease. Methods: Hepcidin wild-type (WT) and KO animals fed 3% carbonyl iron-containing chow were compared to mice kept on standard diet. Liver histology and serum parameters were employed to assess the extent of liver injury/fibrosis. Iron distribution was determined by subcellular fractionation and electron microscopy. Results: Among mice kept on iron-rich diet, 6 month old hepcidin KOs (vs. WTs) displayed profound hepatic iron overload (2543±114 vs. 1493±136p<0,005), elevated liver enzyme (AST: KO 261±15, WT 142±34p<0,05) and serum iron levels, mild hepatocellular inflammation and apoptosis. 12, but not 6 month old KOs fed iron-rich diet developed moderate liver fibrosis as determined by Sirius red staining and increased hydroxyproline levels. The liver injury was likely due to a marked lysosomal iron overload and lysosomal fragility with release of cathepsins into the cytoplasm, while no increased lipid peroxidation or protein carbonylation was noted. As a potential mechanism, the expression of DMT1 and STEAP3, i.e. the molecules needed for lysosomal iron export, was greatly reduced. Conclusions: Hepcidin KOs represent a unique tool to study the mechanism of iron overload-related liver diseases and implicate lysosomal injury as a crucial event in iron toxicity.