Intestinal ferroportin protein expression in murine models of hemojuvelin overexpression

Isabelle HORNUNG1, Ingrid FLEMING2, Frank ROSENBAUER4, Kai ZACHAROWSKI1, Lisa SCHRADER1,3, Andrea STEINBICKER1,3, Deniz DOGAN1, Rüdiger POPP2, Eugen URZICA3, David OGUAMA3, Franca FETTE1,3, Lien NGUYEN3, Paul LOICK1,3, Marcel RAUER1,3

1Department of Anaesthesiology, Intensive Care Medicine and Pain Therapy, University Hospital Frankfurt, Goethe University Frankfurt, Frankfurt am Main, Germany
2Department of Molecular Medicine, Institute of Vascular Signaling, Goethe University Frankfurt, Frankfurt am Main, Germany
3Department of Anaesthesiology, Intensive Care and Pain Medicine, University Hospital Muenster, University of Muenster, Muenster, Germany
4Institute of Molecular Tumor Biology, University Hospital Muenster, University of Muenster, Muenster, Germany

The hepatic hormone hepcidin is the key regulator of systemic iron homeostasis. It acts on intestinal iron absorption through the negative post translational regulation of the iron exporter ferroportin in enterocytes. Hepcidin expression is mainly regulated via the BMP/SMAD signaling pathway and induced by the BMP co-receptor hemojuvelin (HJV) under physiological conditions. In the current experiment, we investigated the interaction of HJV with the BMP type I receptor ALK3. We used an established model of adeno-associated virus (AAV) to overexpress HJV in hepatocyte-specific Alk3 deficient mice and appropriate controls. Mice with hepatocyte-specific ALK3 deficiency present with severe iron overload and hepcidin deficiency. The hepatocyte-specific Alk3 deficiency and HJV overexpression was confirmed by qPCR. Subsidiary, immunoblotting showed liver specific increased HJV in AAV-injected mice. In control mice, HJV overexpression led to increased hepatic Hamp mRNA levels. In contrast, in Alk3fl/fl;Alb-Cre mice with AAV-HJV, hepcidin mRNA levels decreased to an even lower level. In addition, effects of HJV overexpression on ferroportin were determined in histological stainings. In the intestine of Alk3fl/fl;Alb-Cre mice, ferroportin was increased compared to controls. Administration of HJV reduced ferroportin in Alk3fl/fl mice, while there was a slight increase of ferroportin in Alk3fl/fl;Alb-Cre mice compared to respective PBS-injected controls. To determine erythropoiesis in the setting of HJV overexpression, bone marrow was analyzed via FACS. There was no change in erythropoiesis. To conclude, the data indicate that HJV mediates the activation of BMP/SMAD signaling via ALK3 in vivo.