Changes in gene expression of cholesterol metabolism pathways in mouse models of haemochromatosis
Graham, R., Delima, R.D., Johnstone, D., Milward, E.A., Olynyk, J.K. and Trinder, D. (2013) Changes in gene expression of cholesterol metabolism pathways in mouse models of haemochromatosis. In: BioIron 2013, 14 - 18 April 2013, University College, London.
Introduction: The liver is central to the metabolism of both iron and cholesterol. Cholesterol is synthesised and further metabolised to bile acids in the liver and the liver plays an important role in regulation of iron metabolism. It is also the organ in which excess iron is stored. Clinically, links have been noted between lipid and iron metabolism, with approximately one - third of patients with non - alcoholic fatty liver disease exhibiting altered iron parameters. On a molecular level, we have previously reported that wild - type mice fed iron - deficient, normal or iron - loaded diets exhibited increased hepatic cholesterol and increased hepatic gene expression of enzymes in the cholesterol biosynthesis pathway with increasing hepatic iron burden. In the genetic disorder, haemochromatosis, the liver can become overloaded with iron; however, clinical studies have suggested that lipid metabolism may not be perturbed in haemochromatosis.
Methods and Materials: We investigated hepatic cholesterol metabolis m in three mouse models of hereditary haemochromatosis: Hfe - / - , Tfr2 Y245X single mutant and Hfe - / - x Tfr2 Y245X double mutant animals as well as wild - type controls. Mice were fed normal mouse chow and sacrificed at 10 weeks of age. Hepatic gene expression, total cholesterol and non – haem iron were measured. Liver non - haem iron was similar in Hfe - / - and Tfr2 Y245X mice (16.6±0.8 and 17±1 μmol Fe /g liver, respectively) and significantly higher in the double mutant animals (22.4±0.7 μmol Fe /g liver ; P<0.004) than either of the single mutant mice.
Results: Only one group of genes increased significantly with increasing hepatic iron: those involved in cholesterol transport. Gene expression of apolipoproteins A4, C1, C2, C3 and E increased significantly with increasing hepatic iron as did expression of VLDL receptor. In contrast to our findings in wild - type mice, gene expression of cholesterol biosynthetic enzymes did not increase significantly with liver iron burden and there were no differences in hepatic cholesterol between the groups of mutant mice. We also measured expression of genes involved in cholesterol regulation, which similarly, did not increase with increasing hepatic iron. Approximately 50% of cholesterol synthesised in the liver is directed to bile acid synthesis; however, gene expression of bile acid pathway enzymes did not change with respect to hepatic iron burden. Conclusion: These results suggest that iron - associated cholesterol regulation may be ameliorated by the genetic changes which occur in haemochromatosis.
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|Murdoch Affiliation:||Institute for Immunology and Infectious Diseases|
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