BONE PHENOTYPING OF MURINE HEMOCHROMATOSIS MODELS WITH DEFICIENCIES OF HJV-, ALK2 OR ALK3

Deniz Yildirim DOGAN1, Andrea U STEINBICKER1, Isabelle HORNUNG1, Mariateresa PETTINATO2, Alessia PAGANI2, Ulrike BASCHANT3, Guiscard SEEBOHM4, Lorenz C HOFBAUER3, Laura SILVESTRI2,6, Martina RAUNER3

1Department of Anesthesia, Intensive Care and Pain Medicine, Goethe University Frankfurt, Frankfurt am Main, Germany
2Regulation of Iron Metabolism Unit, Division of Genetics and Cell Biology,, IRCCS San Raffaele Scientific Institute, Milan, Italy
3Department of Medicine III & Center for Healthy Aging, Technische Universität Dresden,, Dresden, Germany
4IfGH–Cellular Electrophysiology, Department of Cardiology and Angiology, University Hospital of Münster,, Münster, Germany
5Department of Psychiatry and Psychotherapy, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
6School of Medicine, Vita-Salute San Raffaele University, Milan, Italy

Osteopenia is observed in patients with iron overload, especially in HFE-dependent hereditary hemochromatosis (HH). While some mouse models of Hfe-HH show bone loss, this phenotype has not always been confirmed. Here, we assessed the bone phenotype of additional mouse models of iron overload, Hjv-/- mice and hepatocyte-specific Alk2 or Alk3 deficient mice to clarify under which circumstances high iron levels lead to bone loss. Bone phenotypes of 12-week-old mice with a global deletion of Hjv and hepatocyte-specific Alk2 and Alk3 deficient mice were investigated. Male Alk2fl/fl;Alb-Cre mice were additionally raised on an iron-deficient diet to investigate the role of iron overload. Bone microarchitecture was examined using µCT. Bone remodeling was assessed using histomorphometry and serum bone turnover markers. Male and female Hjv-/- mice and female Alk2fl/fl;Alb-Cre and Alk3fl/fl;Alb-Cre had no altered trabecular or cortical bone mass or bone turnover, despite iron overload. Male Alk2fl/fl;Alb-Cre and Alk3fl/fl;Alb-Cre mice also presented with a regular trabecular bone mass at all ages, albeit 6-month-old Alk3fl/fl;Alb-Cre mice showed an increased number of osteoclasts (+30%) and a lower bone formation rate (-50%). Cortical thickness of the femur was reduced in 6-month-old male Alk2fl/fl;Alb-Cre and Alk3fl/fl;Alb-Cre mice. Raising Alk2fl/fl;Alb-Cre mice on an iron-deficient diet rescued the cortical bone phenotype. 

Cortical bone was affected in male Alk2fl/fl;Alb-Cre and Alk3fl/fl;Alb-Cre mice, suggesting specific roles for Alk2 and Alk3 in iron regulation of cortical bone that may be sex-specific. Whether the lack of trabecular bone loss is related to the relative hepcidin deficiency in these models remains to be investigated.