Postnatal deletion of β-catenin in osterix-expressing cells is necessary for bone growth and intermittent PTH-induced bone gain

wnt/β-catenin signaling has been shown to influence bone homeostasis and is important for parathyroid hormone (PTH)-induced bone gain. To further understand the role of β-catenin in the early stages of osteoblastic lineage cells for postnatal bone homeostasis and the anabolic actions of PTH on bone, we examined mice with postnatal disruption of β-catenin in osterix-expressing cells (β-catenin KO mice) by mating floxed β-catenin mice with transgenic mice expressing cre under the control of the osterix promoter suppressible by doxycycline. After withdrawal of doxycycline, β-catenin KO mice developed progressive bone loss, ectopic cartilage formation, accumulation of mesenchymal stromal cells, and bone marrow adiposity. The β-catenin-defective osteoblasts sorted by flow cytometry from β-catenin KO mice exhibited decreased EdU incorporation, increased annexin V activity, and profound alterations in gene expression including wnt target genes, osteoclast regulators, and osteoblast markers. A dramatic increase in osteoclasts was observed in both neonatal and postnatal β-catenin KO mice. Intermittent administration of PTH for 4 weeks significantly increased bone mass in control mice; however, this anabolic effect of PTH was substantially blunted in β-catenin KO mice. Our data indicate that β-catenin in osterix-expressing cells is required for postnatal osteoblast differentiation, osteoblast proliferation, and bone resorption, and is essential for the anabolic actions of PTH in bone.