Bone Abstracts (2016) 5 OC2.2 | DOI: 10.1530/boneabs.5.OC2.2

Deletion of Dickkopf-1 in osteoblasts or osteocytes increases bone volume in female mice

Sylvia Thiele1, Ulrike Baschant1, Stefanie Thiele1, Christof Niehrs2,3, Lynda Bonewald4, Lorenz C Hofbauer1,5 & Martina Rauner1


1Division of Endocrinology and Metabolic Bone Diseases, Department of Medicine III, Technische Universität Dresden, Dresden, Germany; 2Division of Molecular Embryology, DKFZ-ZMBH Alliance, Heidelberg, Germany; 3Institute of Molecular Biology, Mainz, Germany; 4Bone Biology/Mineralized Tissue Research Program, Department of Oral and Craniofacial Sciences, UMKC School of Dentistry, Kansas City, Missouri, USA; 5DFG Research Center and Cluster of Excellence for Regenerative Therapies, Technische Universität Dresden, Dresden, Germany.


Osteoporosis is a frequent disease leading to an increased risk of fractures caused by a systemic impairment of bone mass, strength, and microarchitecture. Given the emerging role of the Wnt signaling pathway in bone biology, we focused on the function of the important Wnt inhibitor dickkopf-1 (Dkk-1) and examined how the deletion of Dkk-1 solely in osteoblasts or osteocytes influences bone homeostasis. Therefore, we used the Cre-LoxP recombination system and crossed Dkk-1-floxed mice with osterix-cre (Osx; osteoblast-specific) and dentin matrix protein1-cre (Dmp-1; osteocyte-specific) mice. Female and male mice were examined at 10–12 weeks of age. However, the male mice did not show significant differences. Female mice without Dkk-1 in their osteoblasts showed a 3.75-fold increase in bone volume/total volume (BV/TV) compared to cre-negative controls. Furthermore, the trabecular number was increased by 59%, while the trabecular separation decreased by 38%. Cortical thickness and density were not changed. The deletion of Dkk-1 in osteoblasts seemed to have a significant impact on the amount of Dkk-1 in the serum as Dkk-1OsxCre mice had markedly lower Dkk-1 serum levels (−77%) compared to controls, whereas Dkk-1 serum levels were not changed in Dkk-1Dmp1Cre mice. However, Dkk-1Dmp1Cre mice also showed a significant increase in the BV/TV (twofold), the trabecular number (+33%), and the cortical thickness (+9%) while the separation was reduced (−26%). Histomorphometric parameters underlined these results as the mineral apposition rate and the bone formation rate were increased in both mouse lines. In summary, we show that most systemic Dkk-1 stems from osteoblasts and not from osteocytes. Nevertheless, the amount of Dkk-1 in osteoblasts and osteocytes is sufficient to modulate bone mass. Thus, the individual contribution of each cell type to the pathogenesis of specific bone diseases such as post-menopausal osteoporosis should be further investigated to potentially specifically target Dkk-1.

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