Disruption of hemochromatosis protein and transferrin receptor 2 causes iron-induced liver injury in mice

Abstract

Mutations in hemochromatosis protein (HFE) or transferrin receptor 2 (TFR2) cause hereditary hemochromatosis (HH) by impeding production of the liver iron-regulatory hormone, hepcidin (HAMP). This study examined the effects of disruption of Hfe or Tfr2, either alone or together, on liver iron loading and injury in mouse models of HH. Iron status was determined in Hfe knockout (Hfe 2/2 ), Tfr2 Y245X mutant (Tfr2 mut ), and doublemutant (Hfe 2/2 3Tfr2 mut ) mice by measuring plasma and liver iron levels. Plasma alanine transaminase (ALT) activity, liver histology, and collagen deposition were evaluated to assess liver injury. Hepatic oxidative stress was assessed by measuring superoxide dismutase (SOD) activity and F 2 -isoprostane levels. Gene expression was measured by real-time polymerase chain reaction. Hfe 2/2 3Tfr2 mut mice had elevated hepatic iron with a periportal distribution and increased plasma iron, transferrin saturation, and non-transferrin-bound iron, compared with Hfe 2/2 , Tfr2 mut , and wild-type (WT) mice. Hamp1 expression was reduced to 40% (Hfe 2/2 and Tfr2 mut ) and 1% (Hfe 2/2 3Tfr2 mut ) of WT values. Hfe 2/2 3Tfr2 mut mice had elevated plasma ALT activity and mild hepatic inflammation with scattered aggregates of infiltrating inflammatory cluster of differentiation 45 (CD45)-positive cells. Increased hepatic hydoxyproline levels as well as Sirius red and Masson's Trichrome staining demonstrated advanced portal collagen deposition. Hfe 2/2 and Tfr2 mut mice had less hepatic inflammation and collagen deposition. Liver F 2 -isoprostane levels were elevated, and copper/zinc and manganese SOD activities decreased in Hfe 2/2 3Tfr2 mut , Tfr2 mut , and Hfe 2/2 mice, compared with WT mice. Conclusion: Disruption of both Hfe and Tfr2 caused more severe hepatic iron overload with more advanced lipid peroxidation, inflammation, and portal fibrosis than was observed with the disruption of either gene alone. The Hfe 2/2 3Tfr2 mut mouse model of iron-induced liver injury reflects the liver injury phenotype observed in human HH. (HEPATOLOGY 2012;56:585-593)

Transcription factor NRF2 protects mice against dietary iron-induced liver injury by preventing hepatocytic cell death

“…The fact that Nrf2 -/-mice fed iron-rich diet develop marked liver injury despite a similar hepatic iron loading to wild-type animals is of great relevance because although the liver is particularly exposed to the toxic effects of iron in excess, rodents are generally resistant to iron-induced liver injury. Mouse models of HH develop the spontaneous iron overload phenotype seen in human patients without developing significant iron-induced liver injury [27,28]. Likewise, the supplementation of mouse diets with carbonyl iron is generally well tolerated, despite the substantial increase in hepatic iron [5,29].…”

Hepcidin knockout mice as a model of iron-overload associated liver disease

“…On the other hand, values observed in hepcidin knockout mice fed iron-rich diet are higher than values seen in other animal models of iron overload, such as HFE KO, TFR2 KO and HFE -/-/TFR2 mut [144]. For example, HFE/TFR2 double knockout mice displayed serum NTBI level of approximately 9 µM, while HFE and TFR2 knockout mice showed even lower serum NTBI of approximately 3-4 µM [144].…”

“…In conclusion, the particularly high extent of iron accumulation in hepcidin knockout mice which is evidenced by high NTBIs, ferritin, and liver iron levels likely contributes to the development of liver injury in hepcidin knockout mouse model as it has been observed in HH subjects [144,145].…”

“…On the other hand, no apparent inflammation was seen in HFE KO mice and TFR2 mut mice fed iron-rich diet [144]. Interestingly, both mouse lines showed a predominantly mononuclear infiltration, which is reminiscent of HH subjects, who present with a similar picture and in whom the presence of inflammation associates with liver fibrosis development [146,147].…”

“…With respect to the histological signs of liver injury, hepcidin KO mice fed with iron-rich, but not normal diet displayed mild liver inflammation, which was also observed in HFE -/-/TFR2 mut mice [144]. On the other hand, no apparent inflammation was seen in HFE KO mice and TFR2 mut mice fed iron-rich diet [144].…”