Effect of phlebotomy on hepcidin expression in hemojuvelin-mutant mice

Hemojuvelin (Hjv) is an essential component of the pathway regulating hepcidin (Hamp1) gene expression. Mice with targeted disruption of the Hjv gene (Hjv-/- mice) fail to upregulate hepatic Hamp1 expression following iron overload. The main aim of the study was to determine whether the Hjv protein is also necessary for Hamp1 downregulation. In addition, sex differences in Hamp1 expression in Hjv-/- mice were also examined. Male and female Hjv-/- mice (129SvJ background) were used for the experiments, tissue Hamp1 and Hamp2 mRNA content was determined by real-time PCR. Hepatic Hamp1 mRNA content in male Hjv-/- mice was low (0.6% of Hjv+/+ males), however, female Hjv-/- mice displayed only moderately reduced (to 17%) Hamp1 mRNA levels. Hepatic non-heme iron concentration was similar in Hjv-/- mice of both sexes. Disruption of the Hjv gene did not affect Hamp1 mRNA content in the myocardium or Hamp2 mRNA content in the pancreas. Single phlebotomy resulted in significant reduction of Hamp1 mRNA in both male and female Hjv+/+ mice (to 17% and 27% of controls respectively), measured 20 h after treatment. In Hjv-/- mice, phlebotomy decreased Hamp1 mRNA content to 46% in males and to 11% in females. Bleeding also significantly decreased (to 16%) hepatic Hamp2 mRNA levels in Hjv-/- females. The obtained results indicate that the pathway mediating hepcidin downregulation by phlebotomy does not require functional hemojuvelin protein. In addition, they confirm a significant effect of sex on hepcidin gene expression.